diff --git a/spec/unit/webrtc/callEventHandler.spec.ts b/spec/unit/webrtc/callEventHandler.spec.ts
index e9bbeea28..d6012a7a2 100644
--- a/spec/unit/webrtc/callEventHandler.spec.ts
+++ b/spec/unit/webrtc/callEventHandler.spec.ts
@@ -99,7 +99,7 @@ describe("CallEventHandler", () => {
 
         expect(callEventHandler.callEventBuffer.length).toBe(2);
         expect(callEventHandler.nextSeqByCall.get("123")).toBe(2);
-        expect(callEventHandler.toDeviceEventBuffers.get("123").length).toBe(1);
+        expect(callEventHandler.toDeviceEventBuffers.get("123")?.length).toBe(1);
 
         const event4 = new MatrixEvent({
             type: EventType.CallCandidates,
@@ -112,7 +112,7 @@ describe("CallEventHandler", () => {
 
         expect(callEventHandler.callEventBuffer.length).toBe(2);
         expect(callEventHandler.nextSeqByCall.get("123")).toBe(2);
-        expect(callEventHandler.toDeviceEventBuffers.get("123").length).toBe(2);
+        expect(callEventHandler.toDeviceEventBuffers.get("123")?.length).toBe(2);
 
         const event5 = new MatrixEvent({
             type: EventType.CallCandidates,
@@ -125,7 +125,7 @@ describe("CallEventHandler", () => {
 
         expect(callEventHandler.callEventBuffer.length).toBe(5);
         expect(callEventHandler.nextSeqByCall.get("123")).toBe(5);
-        expect(callEventHandler.toDeviceEventBuffers.get("123").length).toBe(0);
+        expect(callEventHandler.toDeviceEventBuffers.get("123")?.length).toBe(0);
     });
 
     it("should ignore a call if invite & hangup come within a single sync", () => {
@@ -161,7 +161,7 @@ describe("CallEventHandler", () => {
     it("should ignore non-call events", async () => {
         // @ts-ignore Mock handleCallEvent is private
         jest.spyOn(client.callEventHandler, "handleCallEvent");
-        jest.spyOn(client, "checkTurnServers").mockReturnValue(undefined);
+        jest.spyOn(client, "checkTurnServers").mockReturnValue(Promise.resolve(true));
 
         const room = new Room("!room:id", client, "@user:id");
         const timelineData: IRoomTimelineData = { timeline: new EventTimeline(new EventTimelineSet(room, {})) };
@@ -186,10 +186,10 @@ describe("CallEventHandler", () => {
         let room: Room;
 
         beforeEach(() => {
-            room = new Room("!room:id", client, client.getUserId());
+            room = new Room("!room:id", client, client.getUserId()!);
             timelineData = { timeline: new EventTimeline(new EventTimelineSet(room, {})) };
 
-            jest.spyOn(client, "checkTurnServers").mockReturnValue(undefined);
+            jest.spyOn(client, "checkTurnServers").mockReturnValue(Promise.resolve(true));
             jest.spyOn(client, "getRoom").mockReturnValue(room);
             jest.spyOn(room, "getMember").mockReturnValue({ user_id: client.getUserId() } as unknown as RoomMember);
 
@@ -246,10 +246,10 @@ describe("CallEventHandler", () => {
             await sync();
 
             expect(incomingCallListener).toHaveBeenCalled();
-            expect(call.groupCallId).toBe(GROUP_CALL_ID);
+            expect(call!.groupCallId).toBe(GROUP_CALL_ID);
             // @ts-ignore Mock opponentDeviceId is private
             expect(call.opponentDeviceId).toBe(DEVICE_ID);
-            expect(call.getOpponentSessionId()).toBe(SESSION_ID);
+            expect(call!.getOpponentSessionId()).toBe(SESSION_ID);
             // @ts-ignore Mock onIncomingCall is private
             expect(groupCall.onIncomingCall).toHaveBeenCalledWith(call);
 
diff --git a/spec/unit/webrtc/groupCall.spec.ts b/spec/unit/webrtc/groupCall.spec.ts
index ae95e4c86..75b75c2e4 100644
--- a/spec/unit/webrtc/groupCall.spec.ts
+++ b/spec/unit/webrtc/groupCall.spec.ts
@@ -116,8 +116,8 @@ class MockCall {
         setAudioVideoMuted: jest.fn<void, [boolean, boolean]>(),
         stream: new MockMediaStream("stream"),
     };
-    public remoteUsermediaFeed: CallFeed;
-    public remoteScreensharingFeed: CallFeed;
+    public remoteUsermediaFeed?: CallFeed;
+    public remoteScreensharingFeed?: CallFeed;
 
     public reject = jest.fn<void, []>();
     public answerWithCallFeeds = jest.fn<void, [CallFeed[]]>();
@@ -128,7 +128,7 @@ class MockCall {
     on = jest.fn();
     removeListener = jest.fn();
 
-    getOpponentMember() {
+    getOpponentMember(): Partial<RoomMember> {
         return {
             userId: this.opponentUserId,
         };
@@ -276,7 +276,7 @@ describe('Group Call', function() {
 
                 await groupCall.initLocalCallFeed();
 
-                const oldStream = groupCall.localCallFeed.stream as unknown as MockMediaStream;
+                const oldStream = groupCall.localCallFeed?.stream as unknown as MockMediaStream;
 
                 // arbitrary values, important part is that they're the same afterwards
                 await groupCall.setLocalVideoMuted(true);
@@ -286,7 +286,7 @@ describe('Group Call', function() {
 
                 groupCall.updateLocalUsermediaStream(newStream);
 
-                expect(groupCall.localCallFeed.stream).toBe(newStream);
+                expect(groupCall.localCallFeed?.stream).toBe(newStream);
 
                 expect(groupCall.isLocalVideoMuted()).toEqual(true);
                 expect(groupCall.isMicrophoneMuted()).toEqual(false);
@@ -474,7 +474,7 @@ describe('Group Call', function() {
                 // we should still be muted at this point because the metadata update hasn't sent
                 expect(groupCall.isMicrophoneMuted()).toEqual(true);
                 expect(mockCall.localUsermediaFeed.setAudioVideoMuted).not.toHaveBeenCalled();
-                metadataUpdateResolve();
+                metadataUpdateResolve!();
 
                 await mutePromise;
 
@@ -500,7 +500,7 @@ describe('Group Call', function() {
                 // we should be muted at this point, before the metadata update has been sent
                 expect(groupCall.isMicrophoneMuted()).toEqual(true);
                 expect(mockCall.localUsermediaFeed.setAudioVideoMuted).toHaveBeenCalled();
-                metadataUpdateResolve();
+                metadataUpdateResolve!();
 
                 await mutePromise;
 
@@ -550,7 +550,7 @@ describe('Group Call', function() {
                     groupCall1.onMemberStateChanged(fakeEvent);
                     groupCall2.onMemberStateChanged(fakeEvent);
                 }
-                return Promise.resolve(null);
+                return Promise.resolve({ "event_id": "foo" });
             };
 
             client1.sendStateEvent.mockImplementation(fakeSendStateEvents);
@@ -644,7 +644,7 @@ describe('Group Call', function() {
                 expect(client1.sendToDevice).toHaveBeenCalled();
 
                 const oldCall = groupCall1.getCallByUserId(client2.userId);
-                oldCall.emit(CallEvent.Hangup, oldCall);
+                oldCall!.emit(CallEvent.Hangup, oldCall!);
 
                 client1.sendToDevice.mockClear();
 
@@ -660,11 +660,11 @@ describe('Group Call', function() {
                 // when we placed the call, we could await on enter which waited for the call to
                 // be made. We don't have that luxury now, so first have to wait for the call
                 // to even be created...
-                let newCall: MatrixCall;
+                let newCall: MatrixCall | undefined;
                 while (
                     (newCall = groupCall1.getCallByUserId(client2.userId)) === undefined ||
                     newCall.peerConn === undefined ||
-                    newCall.callId == oldCall.callId
+                    newCall.callId == oldCall!.callId
                 ) {
                     await flushPromises();
                 }
@@ -704,7 +704,7 @@ describe('Group Call', function() {
                 groupCall1.setMicrophoneMuted(false);
                 groupCall1.setLocalVideoMuted(false);
 
-                const call = groupCall1.getCallByUserId(client2.userId);
+                const call = groupCall1.getCallByUserId(client2.userId)!;
                 call.isMicrophoneMuted = jest.fn().mockReturnValue(true);
                 call.setMicrophoneMuted = jest.fn();
                 call.isLocalVideoMuted = jest.fn().mockReturnValue(true);
@@ -743,13 +743,13 @@ describe('Group Call', function() {
             it("should mute local audio when calling setMicrophoneMuted()", async () => {
                 const groupCall = await createAndEnterGroupCall(mockClient, room);
 
-                groupCall.localCallFeed.setAudioVideoMuted = jest.fn();
+                groupCall.localCallFeed!.setAudioVideoMuted = jest.fn();
                 const setAVMutedArray = groupCall.calls.map(call => {
-                    call.localUsermediaFeed.setAudioVideoMuted = jest.fn();
-                    return call.localUsermediaFeed.setAudioVideoMuted;
+                    call.localUsermediaFeed!.setAudioVideoMuted = jest.fn();
+                    return call.localUsermediaFeed!.setAudioVideoMuted;
                 });
-                const tracksArray = groupCall.calls.reduce((acc, call) => {
-                    acc.push(...call.localUsermediaStream.getAudioTracks());
+                const tracksArray = groupCall.calls.reduce((acc: MediaStreamTrack[], call: MatrixCall) => {
+                    acc.push(...call.localUsermediaStream!.getAudioTracks());
                     return acc;
                 }, []);
                 const sendMetadataUpdateArray = groupCall.calls.map(call => {
@@ -759,8 +759,8 @@ describe('Group Call', function() {
 
                 await groupCall.setMicrophoneMuted(true);
 
-                groupCall.localCallFeed.stream.getAudioTracks().forEach(track => expect(track.enabled).toBe(false));
-                expect(groupCall.localCallFeed.setAudioVideoMuted).toHaveBeenCalledWith(true, null);
+                groupCall.localCallFeed!.stream.getAudioTracks().forEach(track => expect(track.enabled).toBe(false));
+                expect(groupCall.localCallFeed!.setAudioVideoMuted).toHaveBeenCalledWith(true, null);
                 setAVMutedArray.forEach(f => expect(f).toHaveBeenCalledWith(true, null));
                 tracksArray.forEach(track => expect(track.enabled).toBe(false));
                 sendMetadataUpdateArray.forEach(f => expect(f).toHaveBeenCalled());
@@ -771,14 +771,14 @@ describe('Group Call', function() {
             it("should mute local video when calling setLocalVideoMuted()", async () => {
                 const groupCall = await createAndEnterGroupCall(mockClient, room);
 
-                groupCall.localCallFeed.setAudioVideoMuted = jest.fn();
+                groupCall.localCallFeed!.setAudioVideoMuted = jest.fn();
                 const setAVMutedArray = groupCall.calls.map(call => {
-                    call.localUsermediaFeed.setAudioVideoMuted = jest.fn();
-                    call.localUsermediaFeed.isVideoMuted = jest.fn().mockReturnValue(true);
-                    return call.localUsermediaFeed.setAudioVideoMuted;
+                    call.localUsermediaFeed!.setAudioVideoMuted = jest.fn();
+                    call.localUsermediaFeed!.isVideoMuted = jest.fn().mockReturnValue(true);
+                    return call.localUsermediaFeed!.setAudioVideoMuted;
                 });
-                const tracksArray = groupCall.calls.reduce((acc, call) => {
-                    acc.push(...call.localUsermediaStream.getVideoTracks());
+                const tracksArray = groupCall.calls.reduce((acc: MediaStreamTrack[], call: MatrixCall) => {
+                    acc.push(...call.localUsermediaStream!.getVideoTracks());
                     return acc;
                 }, []);
                 const sendMetadataUpdateArray = groupCall.calls.map(call => {
@@ -788,8 +788,8 @@ describe('Group Call', function() {
 
                 await groupCall.setLocalVideoMuted(true);
 
-                groupCall.localCallFeed.stream.getVideoTracks().forEach(track => expect(track.enabled).toBe(false));
-                expect(groupCall.localCallFeed.setAudioVideoMuted).toHaveBeenCalledWith(null, true);
+                groupCall.localCallFeed!.stream.getVideoTracks().forEach(track => expect(track.enabled).toBe(false));
+                expect(groupCall.localCallFeed!.setAudioVideoMuted).toHaveBeenCalledWith(null, true);
                 setAVMutedArray.forEach(f => expect(f).toHaveBeenCalledWith(null, true));
                 tracksArray.forEach(track => expect(track.enabled).toBe(false));
                 sendMetadataUpdateArray.forEach(f => expect(f).toHaveBeenCalled());
@@ -827,9 +827,9 @@ describe('Group Call', function() {
                 ]));
                 call.onSDPStreamMetadataChangedReceived(metadataEvent);
 
-                const feed = groupCall.getUserMediaFeedByUserId(call.invitee);
-                expect(feed.isAudioMuted()).toBe(true);
-                expect(feed.isVideoMuted()).toBe(false);
+                const feed = groupCall.getUserMediaFeedByUserId(call.invitee!);
+                expect(feed!.isAudioMuted()).toBe(true);
+                expect(feed!.isVideoMuted()).toBe(false);
 
                 groupCall.terminate();
             });
@@ -850,9 +850,9 @@ describe('Group Call', function() {
                 ]));
                 call.onSDPStreamMetadataChangedReceived(metadataEvent);
 
-                const feed = groupCall.getUserMediaFeedByUserId(call.invitee);
-                expect(feed.isAudioMuted()).toBe(false);
-                expect(feed.isVideoMuted()).toBe(true);
+                const feed = groupCall.getUserMediaFeedByUserId(call.invitee!);
+                expect(feed!.isAudioMuted()).toBe(false);
+                expect(feed!.isVideoMuted()).toBe(true);
 
                 groupCall.terminate();
             });
diff --git a/src/webrtc/audioContext.ts b/src/webrtc/audioContext.ts
index 10f0dd949..8a9ceb15d 100644
--- a/src/webrtc/audioContext.ts
+++ b/src/webrtc/audioContext.ts
@@ -38,7 +38,7 @@ export const acquireContext = (): AudioContext => {
 export const releaseContext = () => {
     refCount--;
     if (refCount === 0) {
-        audioContext.close();
+        audioContext?.close();
         audioContext = null;
     }
 };
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 961ddcd56..d3d09ba6f 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -331,7 +331,7 @@ function getTransceiverKey(purpose: SDPStreamMetadataPurpose, kind: TransceiverK
  * @param {MatrixClient} opts.client The Matrix Client instance to send events to.
  */
 export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap> {
-    public roomId: string;
+    public roomId?: string;
     public callId: string;
     public invitee?: string;
     public state = CallState.Fledgling;
@@ -361,15 +361,15 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     private transceivers = new Map<TransceiverKey, RTCRtpTransceiver>();
 
     private inviteOrAnswerSent = false;
-    private waitForLocalAVStream: boolean;
+    private waitForLocalAVStream = false;
     private successor?: MatrixCall;
     private opponentMember?: RoomMember;
     private opponentVersion?: number | string;
     // The party ID of the other side: undefined if we haven't chosen a partner
     // yet, null if we have but they didn't send a party ID.
-    private opponentPartyId: string | null;
-    private opponentCaps: CallCapabilities;
-    private iceDisconnectedTimeout: ReturnType<typeof setTimeout>;
+    private opponentPartyId: string | null | undefined;
+    private opponentCaps?: CallCapabilities;
+    private iceDisconnectedTimeout?: ReturnType<typeof setTimeout>;
     private inviteTimeout?: ReturnType<typeof setTimeout>;
     private readonly removeTrackListeners = new Map<MediaStream, () => void>();
 
@@ -384,7 +384,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
     // Perfect negotiation state: https://www.w3.org/TR/webrtc/#perfect-negotiation-example
     private makingOffer = false;
-    private ignoreOffer: boolean;
+    private ignoreOffer = false;
 
     private responsePromiseChain?: Promise<void>;
 
@@ -399,17 +399,21 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     private callLengthInterval?: ReturnType<typeof setInterval>;
     private callLength = 0;
 
-    private opponentDeviceId: string;
-    private opponentDeviceInfo: DeviceInfo;
-    private opponentSessionId: string;
-    public groupCallId: string;
+    private opponentDeviceId?: string;
+    private opponentDeviceInfo?: DeviceInfo;
+    private opponentSessionId?: string;
+    public groupCallId?: string;
 
     constructor(opts: CallOpts) {
         super();
+
         this.roomId = opts.roomId;
         this.invitee = opts.invitee;
         this.client = opts.client;
-        this.forceTURN = opts.forceTURN;
+
+        if (!this.client.deviceId) throw new Error("Client must have a device ID to start calls");
+
+        this.forceTURN = opts.forceTURN ?? false;
         this.ourPartyId = this.client.deviceId;
         this.opponentDeviceId = opts.opponentDeviceId;
         this.opponentSessionId = opts.opponentSessionId;
@@ -448,7 +452,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
      * @param label A human readable label for this datachannel
      * @param options An object providing configuration options for the data channel.
      */
-    public createDataChannel(label: string, options: RTCDataChannelInit) {
+    public createDataChannel(label: string, options: RTCDataChannelInit | undefined) {
         const dataChannel = this.peerConn!.createDataChannel(label, options);
         this.emit(CallEvent.DataChannel, dataChannel);
         return dataChannel;
@@ -458,7 +462,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         return this.opponentMember;
     }
 
-    public getOpponentSessionId(): string {
+    public getOpponentSessionId(): string | undefined {
         return this.opponentSessionId;
     }
 
@@ -570,8 +574,13 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             this.opponentDeviceInfo = new DeviceInfo(this.opponentDeviceId);
             return;
         }
+        // if we've got to this point, we do want to init crypto, so throw if we can't
+        if (!this.client.crypto) throw new Error("Crypto is not initialised.");
+
+        const userId = this.invitee || this.getOpponentMember()?.userId;
+
+        if (!userId) throw new Error("Couldn't find opponent user ID to init crypto");
 
-        const userId = this.invitee || this.getOpponentMember().userId;
         const deviceInfoMap = await this.client.crypto.deviceList.downloadKeys([userId], false);
         this.opponentDeviceInfo = deviceInfoMap[userId][this.opponentDeviceId];
         if (this.opponentDeviceInfo === undefined) {
@@ -749,7 +758,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                     // accumulate which makes the SDP very large very quickly: in fact it only takes
                     // about 6 video tracks to exceed the maximum size of an Olm-encrypted
                     // Matrix event.
-                    const transceiver = this.transceivers.get(tKey);
+                    const transceiver = this.transceivers.get(tKey)!;
 
                     // this is what would allow us to use addTransceiver(), but it's not available
                     // on Firefox yet. We call it anyway if we have it.
@@ -764,10 +773,15 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                     // doesn't yet implement RTCRTPSender.setStreams()
                     // (https://bugzilla.mozilla.org/show_bug.cgi?id=1510802) so we'd have no way to group the
                     // two tracks together into a stream.
-                    const newSender = this.peerConn.addTrack(track, callFeed.stream);
+                    const newSender = this.peerConn!.addTrack(track, callFeed.stream);
 
                     // now go & fish for the new transceiver
-                    this.transceivers.set(tKey, this.peerConn.getTransceivers().find(t => t.sender === newSender));
+                    const newTransciever = this.peerConn!.getTransceivers().find(t => t.sender === newSender);
+                    if (newTransciever) {
+                        this.transceivers.set(tKey, newTransciever);
+                    } else {
+                        logger.warn("Didn't find a matching transceiver after adding track!");
+                    }
                 }
             }
         }
@@ -797,8 +811,8 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             // There is no way to actually remove a transceiver, so this just sets it to inactive
             // (or recvonly) and replaces the source with nothing.
             if (this.transceivers.has(transceiverKey)) {
-                const transceiver = this.transceivers.get(transceiverKey);
-                if (transceiver.sender) this.peerConn.removeTrack(transceiver.sender);
+                const transceiver = this.transceivers.get(transceiverKey)!;
+                if (transceiver.sender) this.peerConn!.removeTrack(transceiver.sender);
             }
         }
 
@@ -850,7 +864,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         if (!this.peerConn) return;
 
         const statsReport = await this.peerConn.getStats();
-        const stats = [];
+        const stats: any[] = [];
         statsReport.forEach(item => {
             stats.push(item);
         });
@@ -917,8 +931,8 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                     this.hangupParty = CallParty.Remote; // effectively
                     this.setState(CallState.Ended);
                     this.stopAllMedia();
-                    if (this.peerConn.signalingState != 'closed') {
-                        this.peerConn.close();
+                    if (this.peerConn!.signalingState != 'closed') {
+                        this.peerConn!.close();
                     }
                     this.emit(CallEvent.Hangup, this);
                 }
@@ -947,7 +961,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
     private shouldAnswerWithMediaType(
         wantedValue: boolean | undefined,
-        valueOfTheOtherSide: boolean | undefined,
+        valueOfTheOtherSide: boolean,
         type: "audio" | "video",
     ): boolean {
         if (wantedValue && !valueOfTheOtherSide) {
@@ -1186,7 +1200,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             for (const transceiver of [audioTransceiver, videoTransceiver]) {
                 // this is slightly mixing the track and transceiver API but is basically just shorthand
                 // for removing the sender.
-                if (transceiver && transceiver.sender) this.peerConn.removeTrack(transceiver.sender);
+                if (transceiver && transceiver.sender) this.peerConn!.removeTrack(transceiver.sender);
             }
 
             this.client.getMediaHandler().stopScreensharingStream(this.localScreensharingStream!);
@@ -1215,9 +1229,9 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
                 const sender = this.transceivers.get(getTransceiverKey(
                     SDPStreamMetadataPurpose.Usermedia, "video",
-                )).sender;
+                ))?.sender;
 
-                sender?.replaceTrack(track);
+                sender?.replaceTrack(track ?? null);
 
                 this.pushNewLocalFeed(stream, SDPStreamMetadataPurpose.Screenshare, false);
 
@@ -1230,8 +1244,8 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             const track = this.localUsermediaStream?.getTracks().find((track) => track.kind === "video");
             const sender = this.transceivers.get(getTransceiverKey(
                 SDPStreamMetadataPurpose.Usermedia, "video",
-            )).sender;
-            sender?.replaceTrack(track);
+            ))?.sender;
+            sender?.replaceTrack(track ?? null);
 
             this.client.getMediaHandler().stopScreensharingStream(this.localScreensharingStream!);
             this.deleteFeedByStream(this.localScreensharingStream!);
@@ -1298,8 +1312,13 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                     `) to peer connection`,
                 );
 
-                const newSender = this.peerConn!.addTrack(track, this.localUsermediaStream);
-                this.transceivers.set(tKey, this.peerConn.getTransceivers().find(t => t.sender === newSender));
+                const newSender = this.peerConn!.addTrack(track, this.localUsermediaStream!);
+                const newTransciever = this.peerConn!.getTransceivers().find(t => t.sender === newSender);
+                if (newTransciever) {
+                    this.transceivers.set(tKey, newTransciever);
+                } else {
+                    logger.warn("Couldn't find matching transceiver for newly added track!");
+                }
             }
         }
     }
@@ -1436,7 +1455,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         const micShouldBeMuted = this.isMicrophoneMuted() || this.remoteOnHold;
         const vidShouldBeMuted = this.isLocalVideoMuted() || this.remoteOnHold;
 
-        logger.log(`call ${this.callId} updateMuteStatus stream ${this.localUsermediaStream.id} micShouldBeMuted ${
+        logger.log(`call ${this.callId} updateMuteStatus stream ${this.localUsermediaStream!.id} micShouldBeMuted ${
             micShouldBeMuted} vidShouldBeMuted ${vidShouldBeMuted}`);
         setTracksEnabled(this.localUsermediaStream!.getAudioTracks(), !micShouldBeMuted);
         setTracksEnabled(this.localUsermediaStream!.getVideoTracks(), !vidShouldBeMuted);
@@ -1463,7 +1482,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         }
 
         if (requestScreenshareFeed) {
-            this.peerConn.addTransceiver("video", {
+            this.peerConn!.addTransceiver("video", {
                 direction: "recvonly",
             });
         }
@@ -1535,7 +1554,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     // bandwidth when transmitting silence
     private mungeSdp(description: RTCSessionDescriptionInit, mods: CodecParamsMod[]): void {
         // The only way to enable DTX at this time is through SDP munging
-        const sdp = parseSdp(description.sdp);
+        const sdp = parseSdp(description.sdp!);
 
         sdp.media.forEach(media => {
             const payloadTypeToCodecMap = new Map<number, string>();
@@ -1570,7 +1589,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                 }
                 if (!found) {
                     media.fmtp.push({
-                        payload: codecToPayloadTypeMap.get(mod.codec),
+                        payload: codecToPayloadTypeMap.get(mod.codec)!,
                         config: extraconfig.join(";"),
                     });
                 }
@@ -1580,13 +1599,13 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     }
 
     private async createOffer(): Promise<RTCSessionDescriptionInit> {
-        const offer = await this.peerConn.createOffer();
+        const offer = await this.peerConn!.createOffer();
         this.mungeSdp(offer, getCodecParamMods(this.isPtt));
         return offer;
     }
 
     private async createAnswer(): Promise<RTCSessionDescriptionInit> {
-        const answer = await this.peerConn.createAnswer();
+        const answer = await this.peerConn!.createAnswer();
         this.mungeSdp(answer, getCodecParamMods(this.isPtt));
         return answer;
     }
@@ -1665,7 +1684,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     };
 
     private onIceGatheringStateChange = (event: Event): void => {
-        logger.debug(`Call ${this.callId} ice gathering state changed to  ${this.peerConn.iceGatheringState}`);
+        logger.debug(`Call ${this.callId} ice gathering state changed to  ${this.peerConn!.iceGatheringState}`);
         if (this.peerConn?.iceGatheringState === 'complete') {
             this.queueCandidate(null);
         }
@@ -1688,10 +1707,12 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
         if (this.opponentPartyId === undefined) {
             // we haven't picked an opponent yet so save the candidates
-            logger.info(`Call ${this.callId} Buffering ${candidates.length} candidates until we pick an opponent`);
-            const bufferedCandidates = this.remoteCandidateBuffer.get(fromPartyId) || [];
-            bufferedCandidates.push(...candidates);
-            this.remoteCandidateBuffer.set(fromPartyId, bufferedCandidates);
+            if (fromPartyId) {
+                logger.info(`Call ${this.callId} Buffering ${candidates.length} candidates until we pick an opponent`);
+                const bufferedCandidates = this.remoteCandidateBuffer.get(fromPartyId) || [];
+                bufferedCandidates.push(...candidates);
+                this.remoteCandidateBuffer.set(fromPartyId, bufferedCandidates);
+            }
             return;
         }
 
@@ -1905,7 +1926,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         try {
             await this.gotLocalOffer();
         } catch (e) {
-            this.getLocalOfferFailed(e);
+            this.getLocalOfferFailed(e as Error);
             return;
         } finally {
             this.makingOffer = false;
@@ -1932,7 +1953,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         }
 
         try {
-            await this.peerConn.setLocalDescription(offer);
+            await this.peerConn!.setLocalDescription(offer);
         } catch (err) {
             logger.debug(`Call ${this.callId} Error setting local description!`, err);
             this.terminate(CallParty.Local, CallErrorCode.SetLocalDescription, true);
@@ -2057,7 +2078,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
         // ideally we'd consider the call to be connected when we get media but
         // chrome doesn't implement any of the 'onstarted' events yet
-        if (["connected", "completed"].includes(this.peerConn?.iceConnectionState)) {
+        if (["connected", "completed"].includes(this.peerConn?.iceConnectionState ?? '')) {
             clearTimeout(this.iceDisconnectedTimeout);
             this.setState(CallState.Connected);
 
@@ -2069,7 +2090,9 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             }
         } else if (this.peerConn?.iceConnectionState == 'failed') {
             // Firefox for Android does not yet have support for restartIce()
-            if (this.peerConn?.restartIce) {
+            // (the types say it's always defined though, so we have to cast
+            // to prevent typescript from warning).
+            if (this.peerConn?.restartIce as (() => void) | null) {
                 this.candidatesEnded = false;
                 this.peerConn!.restartIce();
             } else {
@@ -2085,7 +2108,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         // the peer, since we don't want to block the line if they're not saying anything.
         // Experimenting in Chrome, this happens after 5 or 6 seconds, which is probably
         // fast enough.
-        if (this.isPtt && ["failed", "disconnected"].includes(this.peerConn.iceConnectionState)) {
+        if (this.isPtt && ["failed", "disconnected"].includes(this.peerConn!.iceConnectionState)) {
             for (const feed of this.getRemoteFeeds()) {
                 feed.setAudioVideoMuted(true, true);
             }
@@ -2243,16 +2266,16 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             this.emit(CallEvent.SendVoipEvent, {
                 type: "toDevice",
                 eventType,
-                userId: this.invitee || this.getOpponentMember().userId,
+                userId: this.invitee || this.getOpponentMember()?.userId,
                 opponentDeviceId: this.opponentDeviceId,
                 content,
             });
 
-            const userId = this.invitee || this.getOpponentMember().userId;
+            const userId = this.invitee || this.getOpponentMember()!.userId;
             if (this.client.getUseE2eForGroupCall()) {
                 await this.client.encryptAndSendToDevices([{
                     userId,
-                    deviceInfo: this.opponentDeviceInfo,
+                    deviceInfo: this.opponentDeviceInfo!,
                 }], {
                     type: eventType,
                     content,
@@ -2273,7 +2296,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                 userId: this.invitee || this.getOpponentMember()?.userId,
             });
 
-            await this.client.sendEvent(this.roomId, eventType, realContent);
+            await this.client.sendEvent(this.roomId!, eventType, realContent);
         }
     }
 
@@ -2322,7 +2345,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     // Call this method before sending an invite or answer message
     private discardDuplicateCandidates(): number {
         let discardCount = 0;
-        const newQueue = [];
+        const newQueue: RTCIceCandidate[] = [];
 
         for (let i = 0; i < this.candidateSendQueue.length; i++) {
             const candidate = this.candidateSendQueue[i];
@@ -2647,7 +2670,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             this.opponentPartyId = msg.party_id || null;
         }
         this.opponentCaps = msg.capabilities || {} as CallCapabilities;
-        this.opponentMember = this.client.getRoom(this.roomId).getMember(ev.getSender());
+        this.opponentMember = this.client.getRoom(this.roomId)!.getMember(ev.getSender()) ?? undefined;
     }
 
     private async addBufferedIceCandidates(): Promise<void> {
diff --git a/src/webrtc/callEventHandler.ts b/src/webrtc/callEventHandler.ts
index 6a3d5339d..7c2be58ff 100644
--- a/src/webrtc/callEventHandler.ts
+++ b/src/webrtc/callEventHandler.ts
@@ -16,7 +16,7 @@ limitations under the License.
 
 import { MatrixEvent } from '../models/event';
 import { logger } from '../logger';
-import { CallDirection, CallErrorCode, CallState, createNewMatrixCall, MatrixCall } from './call';
+import { CallDirection, CallError, CallErrorCode, CallState, createNewMatrixCall, MatrixCall } from './call';
 import { EventType } from '../@types/event';
 import { ClientEvent, MatrixClient } from '../client';
 import { MCallAnswer, MCallHangupReject } from "./callEventTypes";
@@ -152,7 +152,7 @@ export class CallEventHandler {
                 this.toDeviceEventBuffers.set(content.call_id, []);
             }
 
-            const buffer = this.toDeviceEventBuffers.get(content.call_id);
+            const buffer = this.toDeviceEventBuffers.get(content.call_id)!;
             const index = buffer.findIndex((e) => e.getContent().seq > content.seq);
 
             if (index === -1) {
@@ -172,7 +172,7 @@ export class CallEventHandler {
             while (nextEvent && nextEvent.getContent().seq === this.nextSeqByCall.get(callId)) {
                 this.callEventBuffer.push(nextEvent);
                 this.nextSeqByCall.set(callId, nextEvent.getContent().seq + 1);
-                nextEvent = buffer.shift();
+                nextEvent = buffer!.shift();
             }
         }
     };
@@ -194,7 +194,7 @@ export class CallEventHandler {
 
         let opponentDeviceId: string | undefined;
 
-        let groupCall: GroupCall;
+        let groupCall: GroupCall | undefined;
         if (groupCallId) {
             groupCall = this.client.groupCallEventHandler.getGroupCallById(groupCallId);
 
@@ -241,7 +241,7 @@ export class CallEventHandler {
                 return; // This invite was meant for another user in the room
             }
 
-            const timeUntilTurnCresExpire = this.client.getTurnServersExpiry() - Date.now();
+            const timeUntilTurnCresExpire = (this.client.getTurnServersExpiry() ?? 0) - Date.now();
             logger.info("Current turn creds expire in " + timeUntilTurnCresExpire + " ms");
             call = createNewMatrixCall(
                 this.client,
@@ -267,10 +267,12 @@ export class CallEventHandler {
             try {
                 await call.initWithInvite(event);
             } catch (e) {
-                if (e.code === GroupCallErrorCode.UnknownDevice) {
-                    groupCall?.emit(GroupCallEvent.Error, e);
-                } else {
-                    logger.error(e);
+                if (e instanceof CallError) {
+                    if (e.code === GroupCallErrorCode.UnknownDevice) {
+                        groupCall?.emit(GroupCallEvent.Error, e);
+                    } else {
+                        logger.error(e);
+                    }
                 }
             }
             this.calls.set(call.callId, call);
@@ -292,7 +294,7 @@ export class CallEventHandler {
                 if (
                     call.roomId === thisCall.roomId &&
                     thisCall.direction === CallDirection.Outbound &&
-                    call.getOpponentMember().userId === thisCall.invitee &&
+                    call.getOpponentMember()?.userId === thisCall.invitee &&
                     isCalling
                 ) {
                     existingCall = thisCall;
diff --git a/src/webrtc/callFeed.ts b/src/webrtc/callFeed.ts
index 170910296..51318c50f 100644
--- a/src/webrtc/callFeed.ts
+++ b/src/webrtc/callFeed.ts
@@ -27,7 +27,7 @@ const SPEAKING_SAMPLE_COUNT = 8; // samples
 
 export interface ICallFeedOpts {
     client: MatrixClient;
-    roomId: string;
+    roomId?: string;
     userId: string;
     stream: MediaStream;
     purpose: SDPStreamMetadataPurpose;
@@ -67,7 +67,7 @@ export class CallFeed extends TypedEventEmitter<CallFeedEvent, EventHandlerMap>
     public speakingVolumeSamples: number[];
 
     private client: MatrixClient;
-    private roomId: string;
+    private roomId?: string;
     private audioMuted: boolean;
     private videoMuted: boolean;
     private localVolume = 1;
@@ -295,8 +295,8 @@ export class CallFeed extends TypedEventEmitter<CallFeedEvent, EventHandlerMap>
         clearTimeout(this.volumeLooperTimeout);
         this.stream?.removeEventListener("addtrack", this.onAddTrack);
         if (this.audioContext) {
-            this.audioContext = null;
-            this.analyser = null;
+            this.audioContext = undefined;
+            this.analyser = undefined;
             releaseContext();
         }
         this._disposed = true;
diff --git a/src/webrtc/groupCall.ts b/src/webrtc/groupCall.ts
index eb122a395..150b71ea3 100644
--- a/src/webrtc/groupCall.ts
+++ b/src/webrtc/groupCall.ts
@@ -9,6 +9,7 @@ import { CallErrorCode,
     MatrixCall,
     setTracksEnabled,
     createNewMatrixCall,
+    CallError,
 } from "./call";
 import { RoomMember } from "../models/room-member";
 import { Room } from "../models/room";
@@ -56,7 +57,7 @@ export type GroupCallEventHandlerMap = {
     [GroupCallEvent.UserMediaFeedsChanged]: (feeds: CallFeed[]) => void;
     [GroupCallEvent.ScreenshareFeedsChanged]: (feeds: CallFeed[]) => void;
     [GroupCallEvent.LocalScreenshareStateChanged]: (
-        isScreensharing: boolean, feed: CallFeed, sourceId: string,
+        isScreensharing: boolean, feed?: CallFeed, sourceId?: string,
     ) => void;
     [GroupCallEvent.LocalMuteStateChanged]: (audioMuted: boolean, videoMuted: boolean) => void;
     [GroupCallEvent.ParticipantsChanged]: (participants: RoomMember[]) => void;
@@ -136,7 +137,7 @@ export enum GroupCallState {
 
 interface ICallHandlers {
     onCallFeedsChanged: (feeds: CallFeed[]) => void;
-    onCallStateChanged: (state: CallState, oldState: CallState) => void;
+    onCallStateChanged: (state: CallState, oldState: CallState | undefined) => void;
     onCallHangup: (call: MatrixCall) => void;
     onCallReplaced: (newCall: MatrixCall) => void;
 }
@@ -232,7 +233,7 @@ export class GroupCall extends TypedEventEmitter<
     }
 
     public getLocalFeeds(): CallFeed[] {
-        const feeds = [];
+        const feeds: CallFeed[] = [];
 
         if (this.localCallFeed) feeds.push(this.localCallFeed);
         if (this.localScreenshareFeed) feeds.push(this.localScreenshareFeed);
@@ -311,11 +312,11 @@ export class GroupCall extends TypedEventEmitter<
             await this.initLocalCallFeed();
         }
 
-        this.addParticipant(this.room.getMember(this.client.getUserId()));
+        this.addParticipant(this.room.getMember(this.client.getUserId()!)!);
 
         await this.sendMemberStateEvent();
 
-        this.activeSpeaker = null;
+        this.activeSpeaker = undefined;
 
         this.setState(GroupCallState.Entered);
 
@@ -343,7 +344,7 @@ export class GroupCall extends TypedEventEmitter<
     private dispose() {
         if (this.localCallFeed) {
             this.removeUserMediaFeed(this.localCallFeed);
-            this.localCallFeed = null;
+            this.localCallFeed = undefined;
         }
 
         if (this.localScreenshareFeed) {
@@ -359,7 +360,7 @@ export class GroupCall extends TypedEventEmitter<
             return;
         }
 
-        this.removeParticipant(this.room.getMember(this.client.getUserId()));
+        this.removeParticipant(this.room.getMember(this.client.getUserId()!)!);
 
         this.removeMemberStateEvent();
 
@@ -367,7 +368,7 @@ export class GroupCall extends TypedEventEmitter<
             this.removeCall(this.calls[this.calls.length - 1], CallErrorCode.UserHangup);
         }
 
-        this.activeSpeaker = null;
+        this.activeSpeaker = undefined;
         clearTimeout(this.activeSpeakerLoopTimeout);
 
         this.retryCallCounts.clear();
@@ -470,7 +471,7 @@ export class GroupCall extends TypedEventEmitter<
                     this.setMicrophoneMuted(true);
                 }, this.pttMaxTransmitTime);
             } else if (muted && !this.isMicrophoneMuted()) {
-                clearTimeout(this.transmitTimer);
+                if (this.transmitTimer !== null) clearTimeout(this.transmitTimer);
                 this.transmitTimer = null;
             }
         }
@@ -502,7 +503,7 @@ export class GroupCall extends TypedEventEmitter<
         }
 
         for (const call of this.calls) {
-            setTracksEnabled(call.localUsermediaFeed.stream.getAudioTracks(), !muted);
+            setTracksEnabled(call.localUsermediaFeed!.stream.getAudioTracks(), !muted);
         }
 
         this.emit(GroupCallEvent.LocalMuteStateChanged, muted, this.isLocalVideoMuted());
@@ -576,7 +577,7 @@ export class GroupCall extends TypedEventEmitter<
                 this.localScreenshareFeed = new CallFeed({
                     client: this.client,
                     roomId: this.room.roomId,
-                    userId: this.client.getUserId(),
+                    userId: this.client.getUserId()!,
                     stream,
                     purpose: SDPStreamMetadataPurpose.Screenshare,
                     audioMuted: false,
@@ -593,7 +594,7 @@ export class GroupCall extends TypedEventEmitter<
 
                 // TODO: handle errors
                 await Promise.all(this.calls.map(call => call.pushLocalFeed(
-                    this.localScreenshareFeed.clone(),
+                    this.localScreenshareFeed!.clone(),
                 )));
 
                 await this.sendMemberStateEvent();
@@ -603,7 +604,10 @@ export class GroupCall extends TypedEventEmitter<
                 if (opts.throwOnFail) throw error;
                 logger.error("Enabling screensharing error", error);
                 this.emit(GroupCallEvent.Error,
-                    new GroupCallError(GroupCallErrorCode.NoUserMedia, "Failed to get screen-sharing stream: ", error),
+                    new GroupCallError(
+                        GroupCallErrorCode.NoUserMedia,
+                        "Failed to get screen-sharing stream: ", error as Error,
+                    ),
                 );
                 return false;
             }
@@ -611,8 +615,8 @@ export class GroupCall extends TypedEventEmitter<
             await Promise.all(this.calls.map(call => {
                 if (call.localScreensharingFeed) call.removeLocalFeed(call.localScreensharingFeed);
             }));
-            this.client.getMediaHandler().stopScreensharingStream(this.localScreenshareFeed.stream);
-            this.removeScreenshareFeed(this.localScreenshareFeed);
+            this.client.getMediaHandler().stopScreensharingStream(this.localScreenshareFeed!.stream);
+            this.removeScreenshareFeed(this.localScreenshareFeed!);
             this.localScreenshareFeed = undefined;
             this.localDesktopCapturerSourceId = undefined;
             await this.sendMemberStateEvent();
@@ -652,8 +656,8 @@ export class GroupCall extends TypedEventEmitter<
             return;
         }
 
-        const opponentMemberId = newCall.getOpponentMember().userId;
-        const existingCall = this.getCallByUserId(opponentMemberId);
+        const opponentMemberId = newCall.getOpponentMember()?.userId;
+        const existingCall = opponentMemberId ? this.getCallByUserId(opponentMemberId) : null;
 
         if (existingCall && existingCall.callId === newCall.callId) {
             return;
@@ -709,7 +713,7 @@ export class GroupCall extends TypedEventEmitter<
         const res = await send();
 
         // Clear the old interval first, so that it isn't forgot
-        clearInterval(this.resendMemberStateTimer);
+        if (this.resendMemberStateTimer !== null) clearInterval(this.resendMemberStateTimer);
         // Resend the state event every so often so it doesn't become stale
         this.resendMemberStateTimer = setInterval(async () => {
             logger.log("Resending call member state");
@@ -720,13 +724,13 @@ export class GroupCall extends TypedEventEmitter<
     }
 
     private async removeMemberStateEvent(): Promise<ISendEventResponse> {
-        clearInterval(this.resendMemberStateTimer);
+        if (this.resendMemberStateTimer !== null) clearInterval(this.resendMemberStateTimer);
         this.resendMemberStateTimer = null;
         return await this.updateMemberCallState(undefined);
     }
 
     private async updateMemberCallState(memberCallState?: IGroupCallRoomMemberCallState): Promise<ISendEventResponse> {
-        const localUserId = this.client.getUserId();
+        const localUserId = this.client.getUserId()!;
 
         const memberState = this.getMemberStateEvents(localUserId)?.getContent<IGroupCallRoomMemberState>();
 
@@ -766,7 +770,7 @@ export class GroupCall extends TypedEventEmitter<
         // The member events may be received for another room, which we will ignore.
         if (event.getRoomId() !== this.room.roomId) return;
 
-        const member = this.room.getMember(event.getStateKey());
+        const member = this.room.getMember(event.getStateKey()!);
         if (!member) {
             logger.warn(`Couldn't find room member for ${event.getStateKey()}: ignoring member state event!`);
             return;
@@ -816,7 +820,7 @@ export class GroupCall extends TypedEventEmitter<
         }, content["m.expires_ts"] - Date.now()));
 
         // Don't process your own member.
-        const localUserId = this.client.getUserId();
+        const localUserId = this.client.getUserId()!;
 
         if (member.userId === localUserId) {
             return;
@@ -860,6 +864,11 @@ export class GroupCall extends TypedEventEmitter<
             },
         );
 
+        if (!newCall) {
+            logger.error("Failed to create call!");
+            return;
+        }
+
         if (existingCall) {
             logger.debug(`Replacing call ${existingCall.callId} to ${member.userId} with ${newCall.callId}`);
             this.replaceCall(existingCall, newCall, CallErrorCode.NewSession);
@@ -884,7 +893,7 @@ export class GroupCall extends TypedEventEmitter<
             );
         } catch (e) {
             logger.warn(`Failed to place call to ${member.userId}!`, e);
-            if (e.code === GroupCallErrorCode.UnknownDevice) {
+            if (e instanceof CallError && e.code === GroupCallErrorCode.UnknownDevice) {
                 this.emit(GroupCallEvent.Error, e);
             } else {
                 this.emit(
@@ -904,7 +913,7 @@ export class GroupCall extends TypedEventEmitter<
         }
     };
 
-    public getDeviceForMember(userId: string): IGroupCallRoomMemberDevice {
+    public getDeviceForMember(userId: string): IGroupCallRoomMemberDevice | undefined {
         const memberStateEvent = this.getMemberStateEvents(userId);
 
         if (!memberStateEvent) {
@@ -931,7 +940,7 @@ export class GroupCall extends TypedEventEmitter<
 
     private onRetryCallLoop = () => {
         for (const event of this.getMemberStateEvents()) {
-            const memberId = event.getStateKey();
+            const memberId = event.getStateKey()!;
             const existingCall = this.calls.find((call) => getCallUserId(call) === memberId);
             const retryCallCount = this.retryCallCounts.get(memberId) || 0;
 
@@ -948,7 +957,7 @@ export class GroupCall extends TypedEventEmitter<
      * Call Event Handlers
      */
 
-    public getCallByUserId(userId: string): MatrixCall {
+    public getCallByUserId(userId: string): MatrixCall | undefined {
         return this.calls.find((call) => getCallUserId(call) === userId);
     }
 
@@ -996,7 +1005,7 @@ export class GroupCall extends TypedEventEmitter<
 
         const onCallFeedsChanged = () => this.onCallFeedsChanged(call);
         const onCallStateChanged =
-            (state: CallState, oldState: CallState) => this.onCallStateChanged(call, state, oldState);
+            (state: CallState, oldState: CallState | undefined) => this.onCallStateChanged(call, state, oldState);
         const onCallHangup = this.onCallHangup;
         const onCallReplaced = (newCall: MatrixCall) => this.replaceCall(call, newCall);
 
@@ -1029,7 +1038,7 @@ export class GroupCall extends TypedEventEmitter<
             onCallStateChanged,
             onCallHangup,
             onCallReplaced,
-        } = this.callHandlers.get(opponentMemberId);
+        } = this.callHandlers.get(opponentMemberId)!;
 
         call.removeListener(CallEvent.FeedsChanged, onCallFeedsChanged);
         call.removeListener(CallEvent.State, onCallStateChanged);
@@ -1095,8 +1104,8 @@ export class GroupCall extends TypedEventEmitter<
         }
     };
 
-    private onCallStateChanged = (call: MatrixCall, state: CallState, _oldState: CallState) => {
-        const audioMuted = this.localCallFeed.isAudioMuted();
+    private onCallStateChanged = (call: MatrixCall, state: CallState, _oldState: CallState | undefined) => {
+        const audioMuted = this.localCallFeed!.isAudioMuted();
 
         if (
             call.localUsermediaStream &&
@@ -1105,7 +1114,7 @@ export class GroupCall extends TypedEventEmitter<
             call.setMicrophoneMuted(audioMuted);
         }
 
-        const videoMuted = this.localCallFeed.isVideoMuted();
+        const videoMuted = this.localCallFeed!.isVideoMuted();
 
         if (
             call.localUsermediaStream &&
@@ -1115,7 +1124,7 @@ export class GroupCall extends TypedEventEmitter<
         }
 
         if (state === CallState.Connected) {
-            this.retryCallCounts.delete(getCallUserId(call));
+            this.retryCallCounts.delete(getCallUserId(call)!);
         }
     };
 
@@ -1177,8 +1186,8 @@ export class GroupCall extends TypedEventEmitter<
     }
 
     private onActiveSpeakerLoop = () => {
-        let topAvg: number;
-        let nextActiveSpeaker: string;
+        let topAvg: number | undefined = undefined;
+        let nextActiveSpeaker: string | undefined = undefined;
 
         for (const callFeed of this.userMediaFeeds) {
             if (callFeed.userId === this.client.getUserId() && this.userMediaFeeds.length > 1) {
@@ -1200,7 +1209,7 @@ export class GroupCall extends TypedEventEmitter<
             }
         }
 
-        if (nextActiveSpeaker && this.activeSpeaker !== nextActiveSpeaker && topAvg > SPEAKING_THRESHOLD) {
+        if (nextActiveSpeaker && this.activeSpeaker !== nextActiveSpeaker && topAvg && topAvg > SPEAKING_THRESHOLD) {
             this.activeSpeaker = nextActiveSpeaker;
             this.emit(GroupCallEvent.ActiveSpeakerChanged, this.activeSpeaker);
         }
diff --git a/src/webrtc/groupCallEventHandler.ts b/src/webrtc/groupCallEventHandler.ts
index e38d7f2b4..86df72289 100644
--- a/src/webrtc/groupCallEventHandler.ts
+++ b/src/webrtc/groupCallEventHandler.ts
@@ -91,7 +91,7 @@ export class GroupCallEventHandler {
     }
 
     private getRoomDeferred(roomId: string): RoomDeferred {
-        let deferred: RoomDeferred = this.roomDeferreds.get(roomId);
+        let deferred = this.roomDeferreds.get(roomId);
         if (deferred === undefined) {
             let resolveFunc: () => void;
             deferred = {
@@ -99,7 +99,7 @@ export class GroupCallEventHandler {
                     resolveFunc = resolve;
                 }),
             };
-            deferred.resolve = resolveFunc;
+            deferred.resolve = resolveFunc!;
             this.roomDeferreds.set(roomId, deferred);
         }
 
@@ -110,7 +110,7 @@ export class GroupCallEventHandler {
         return this.getRoomDeferred(roomId).prom;
     }
 
-    public getGroupCallById(groupCallId: string): GroupCall {
+    public getGroupCallById(groupCallId: string): GroupCall | undefined {
         return [...this.groupCalls.values()].find((groupCall) => groupCall.groupCallId === groupCallId);
     }
 
@@ -135,7 +135,7 @@ export class GroupCallEventHandler {
         }
 
         logger.info("Group call event handler processed room", room.roomId);
-        this.getRoomDeferred(room.roomId).resolve();
+        this.getRoomDeferred(room.roomId).resolve!();
     }
 
     private createGroupCallFromRoomStateEvent(event: MatrixEvent): GroupCall | undefined {
diff --git a/src/webrtc/mediaHandler.ts b/src/webrtc/mediaHandler.ts
index fa337098f..bff633018 100644
--- a/src/webrtc/mediaHandler.ts
+++ b/src/webrtc/mediaHandler.ts
@@ -228,8 +228,8 @@ export class MediaHandler extends TypedEventEmitter<
                 this.localUserMediaStream = stream;
             }
         } else {
-            stream = this.localUserMediaStream.clone();
-            logger.log(`mediaHandler clone userMediaStream ${this.localUserMediaStream.id} new stream ${
+            stream = this.localUserMediaStream!.clone();
+            logger.log(`mediaHandler clone userMediaStream ${this.localUserMediaStream?.id} new stream ${
                 stream.id} shouldRequestAudio ${shouldRequestAudio} shouldRequestVideo ${shouldRequestVideo}`);
 
             if (!shouldRequestAudio) {
@@ -282,12 +282,11 @@ export class MediaHandler extends TypedEventEmitter<
      * @param reusable is allowed to be reused by the MediaHandler
      * @returns {MediaStream} based on passed parameters
      */
-    public async getScreensharingStream(opts: IScreensharingOpts = {}, reusable = true): Promise<MediaStream | null> {
+    public async getScreensharingStream(opts: IScreensharingOpts = {}, reusable = true): Promise<MediaStream> {
         let stream: MediaStream;
 
         if (this.screensharingStreams.length === 0) {
             const screenshareConstraints = this.getScreenshareContraints(opts);
-            if (!screenshareConstraints) return null;
 
             if (opts.desktopCapturerSourceId) {
                 // We are using Electron
@@ -385,7 +384,7 @@ export class MediaHandler extends TypedEventEmitter<
         if (desktopCapturerSourceId) {
             logger.debug("Using desktop capturer source", desktopCapturerSourceId);
             return {
-                audio,
+                audio: audio ?? false,
                 video: {
                     mandatory: {
                         chromeMediaSource: "desktop",
@@ -396,7 +395,7 @@ export class MediaHandler extends TypedEventEmitter<
         } else {
             logger.debug("Not using desktop capturer source");
             return {
-                audio,
+                audio: audio ?? false,
                 video: true,
             };
         }