diff --git a/spec/test-utils/webrtc.ts b/spec/test-utils/webrtc.ts
index 6a571b737..e141e6087 100644
--- a/spec/test-utils/webrtc.ts
+++ b/spec/test-utils/webrtc.ts
@@ -101,12 +101,12 @@ export class MockAudioContext {
 export class MockRTCPeerConnection {
     private static instances: MockRTCPeerConnection[] = [];
 
-    private negotiationNeededListener: () => void;
+    private negotiationNeededListener?: () => void;
     public iceCandidateListener?: (e: RTCPeerConnectionIceEvent) => void;
     public onTrackListener?: (e: RTCTrackEvent) => void;
     public needsNegotiation = false;
     public readyToNegotiate: Promise<void>;
-    private onReadyToNegotiate: () => void;
+    private onReadyToNegotiate?: () => void;
     localDescription: RTCSessionDescription;
     signalingState: RTCSignalingState = "stable";
     public transceivers: MockRTCRtpTransceiver[] = [];
@@ -171,7 +171,7 @@ export class MockRTCPeerConnection {
     getStats() { return []; }
     addTransceiver(track: MockMediaStreamTrack): MockRTCRtpTransceiver {
         this.needsNegotiation = true;
-        this.onReadyToNegotiate();
+        if (this.onReadyToNegotiate) this.onReadyToNegotiate();
 
         const newSender = new MockRTCRtpSender(track);
         const newReceiver = new MockRTCRtpReceiver(track);
@@ -190,7 +190,7 @@ export class MockRTCPeerConnection {
 
     removeTrack() {
         this.needsNegotiation = true;
-        this.onReadyToNegotiate();
+        if (this.onReadyToNegotiate) this.onReadyToNegotiate();
     }
 
     getTransceivers(): MockRTCRtpTransceiver[] { return this.transceivers; }
@@ -217,8 +217,8 @@ export class MockRTCRtpReceiver {
 export class MockRTCRtpTransceiver {
     constructor(private peerConn: MockRTCPeerConnection) {}
 
-    public sender: RTCRtpSender;
-    public receiver: RTCRtpReceiver;
+    public sender?: RTCRtpSender;
+    public receiver?: RTCRtpReceiver;
 
     public set direction(_: string) {
         this.peerConn.needsNegotiation = true;
@@ -234,9 +234,9 @@ export class MockMediaStreamTrack {
 
     listeners: [string, (...args: any[]) => any][] = [];
     public isStopped = false;
-    public settings: MediaTrackSettings;
+    public settings?: MediaTrackSettings;
 
-    getSettings(): MediaTrackSettings { return this.settings; }
+    getSettings(): MediaTrackSettings { return this.settings!; }
 
     // XXX: Using EventTarget in jest doesn't seem to work, so we write our own
     // implementation
@@ -409,7 +409,7 @@ export class MockCallMatrixClient extends TypedEventEmitter<EmittedEvents, Emitt
     getUseE2eForGroupCall = () => false;
     checkTurnServers = () => null;
 
-    getSyncState = jest.fn<SyncState, []>().mockReturnValue(SyncState.Syncing);
+    getSyncState = jest.fn<SyncState | null, []>().mockReturnValue(SyncState.Syncing);
 
     getRooms = jest.fn<Room[], []>().mockReturnValue([]);
     getRoom = jest.fn();
diff --git a/spec/unit/webrtc/call.spec.ts b/spec/unit/webrtc/call.spec.ts
index 4d2c50a35..331830d18 100644
--- a/spec/unit/webrtc/call.spec.ts
+++ b/spec/unit/webrtc/call.spec.ts
@@ -169,7 +169,7 @@ describe('Call', function() {
             },
         }));
 
-        const mockAddIceCandidate = call.peerConn.addIceCandidate = jest.fn();
+        const mockAddIceCandidate = call.peerConn!.addIceCandidate = jest.fn();
         call.onRemoteIceCandidatesReceived(makeMockEvent("@test:foo", {
             version: 1,
             call_id: call.callId,
@@ -199,7 +199,7 @@ describe('Call', function() {
 
     it('should add candidates received before answer if party ID is correct', async function() {
         await startVoiceCall(client, call);
-        const mockAddIceCandidate = call.peerConn.addIceCandidate = jest.fn();
+        const mockAddIceCandidate = call.peerConn!.addIceCandidate = jest.fn();
 
         call.onRemoteIceCandidatesReceived(makeMockEvent("@test:foo", {
             version: 1,
@@ -372,12 +372,12 @@ describe('Call', function() {
         // XXX: Lots of inspecting the prvate state of the call object here
         const transceivers: Map<string, RTCRtpTransceiver> = (call as any).transceivers;
 
-        expect(call.localUsermediaStream.id).toBe("stream");
-        expect(call.localUsermediaStream.getAudioTracks()[0].id).toBe("new_audio_track");
-        expect(call.localUsermediaStream.getVideoTracks()[0].id).toBe("video_track");
+        expect(call.localUsermediaStream!.id).toBe("stream");
+        expect(call.localUsermediaStream!.getAudioTracks()[0].id).toBe("new_audio_track");
+        expect(call.localUsermediaStream!.getVideoTracks()[0].id).toBe("video_track");
         // call has a function for generating these but we hardcode here to avoid exporting it
-        expect(transceivers.get("m.usermedia:audio").sender.track.id).toBe("new_audio_track");
-        expect(transceivers.get("m.usermedia:video").sender.track.id).toBe("video_track");
+        expect(transceivers.get("m.usermedia:audio")!.sender.track!.id).toBe("new_audio_track");
+        expect(transceivers.get("m.usermedia:video")!.sender.track!.id).toBe("video_track");
     });
 
     it("should handle upgrade to video call", async () => {
@@ -400,10 +400,10 @@ describe('Call', function() {
         // XXX: More inspecting private state of the call object
         const transceivers: Map<string, RTCRtpTransceiver> = (call as any).transceivers;
 
-        expect(call.localUsermediaStream.getAudioTracks()[0].id).toBe("usermedia_audio_track");
-        expect(call.localUsermediaStream.getVideoTracks()[0].id).toBe("usermedia_video_track");
-        expect(transceivers.get("m.usermedia:audio").sender.track.id).toBe("usermedia_audio_track");
-        expect(transceivers.get("m.usermedia:video").sender.track.id).toBe("usermedia_video_track");
+        expect(call.localUsermediaStream!.getAudioTracks()[0].id).toBe("usermedia_audio_track");
+        expect(call.localUsermediaStream!.getVideoTracks()[0].id).toBe("usermedia_video_track");
+        expect(transceivers.get("m.usermedia:audio")!.sender.track!.id).toBe("usermedia_audio_track");
+        expect(transceivers.get("m.usermedia:video")!.sender.track!.id).toBe("usermedia_video_track");
     });
 
     it("should handle SDPStreamMetadata changes", async () => {
@@ -601,13 +601,13 @@ describe('Call', function() {
         (call as any).pushRemoteFeed(remoteUsermediaStream);
         (call as any).pushRemoteFeed(remoteScreensharingStream);
 
-        expect(call.localUsermediaFeed.stream).toBe(localUsermediaStream);
+        expect(call.localUsermediaFeed!.stream).toBe(localUsermediaStream);
         expect(call.localUsermediaStream).toBe(localUsermediaStream);
-        expect(call.localScreensharingFeed.stream).toBe(localScreensharingStream);
+        expect(call.localScreensharingFeed!.stream).toBe(localScreensharingStream);
         expect(call.localScreensharingStream).toBe(localScreensharingStream);
-        expect(call.remoteUsermediaFeed.stream).toBe(remoteUsermediaStream);
+        expect(call.remoteUsermediaFeed!.stream).toBe(remoteUsermediaStream);
         expect(call.remoteUsermediaStream).toBe(remoteUsermediaStream);
-        expect(call.remoteScreensharingFeed.stream).toBe(remoteScreensharingStream);
+        expect(call.remoteScreensharingFeed!.stream).toBe(remoteScreensharingStream);
         expect(call.remoteScreensharingStream).toBe(remoteScreensharingStream);
         expect(call.hasRemoteUserMediaAudioTrack).toBe(false);
     });
@@ -1214,8 +1214,8 @@ describe('Call', function() {
 
         MockRTCPeerConnection.triggerAllNegotiations();
 
-        const mockVideoSender = call.peerConn.getSenders().find(s => s.track.kind === "video");
-        const mockReplaceTrack = mockVideoSender.replaceTrack = jest.fn();
+        const mockVideoSender = call.peerConn!.getSenders().find(s => s.track!.kind === "video");
+        const mockReplaceTrack = mockVideoSender!.replaceTrack = jest.fn();
 
         await call.setScreensharingEnabled(true);
 
@@ -1336,7 +1336,7 @@ describe('Call', function() {
 
             await call.placeVoiceCall();
 
-            (call.peerConn as unknown as MockRTCPeerConnection).onTrackListener(
+            (call.peerConn as unknown as MockRTCPeerConnection).onTrackListener!(
                 { streams: [], track: new MockMediaStreamTrack("track_ev", "audio") } as unknown as RTCTrackEvent,
             );
 
@@ -1359,7 +1359,7 @@ describe('Call', function() {
             }));
 
             const stream = new MockMediaStream("stream_ev", [new MockMediaStreamTrack("track_ev", "audio")]);
-            (call.peerConn as unknown as MockRTCPeerConnection).onTrackListener(
+            (call.peerConn as unknown as MockRTCPeerConnection).onTrackListener!(
                 { streams: [stream], track: stream.getAudioTracks()[0] } as unknown as RTCTrackEvent,
             );
 
diff --git a/spec/unit/webrtc/callEventHandler.spec.ts b/spec/unit/webrtc/callEventHandler.spec.ts
index d6012a7a2..b7687cdc2 100644
--- a/spec/unit/webrtc/callEventHandler.spec.ts
+++ b/spec/unit/webrtc/callEventHandler.spec.ts
@@ -50,8 +50,8 @@ describe("CallEventHandler", () => {
     });
 
     afterEach(() => {
-        client.callEventHandler.stop();
-        client.groupCallEventHandler.stop();
+        client.callEventHandler!.stop();
+        client.groupCallEventHandler!.stop();
     });
 
     const sync = async () => {
@@ -63,7 +63,7 @@ describe("CallEventHandler", () => {
     };
 
     it("should enforce inbound toDevice message ordering", async () => {
-        const callEventHandler = client.callEventHandler;
+        const callEventHandler = client.callEventHandler!;
         const event1 = new MatrixEvent({
             type: EventType.CallInvite,
             content: {
@@ -227,7 +227,7 @@ describe("CallEventHandler", () => {
             const DEVICE_ID = "device_id";
 
             incomingCallListener.mockImplementation((c) => call = c);
-            jest.spyOn(client.groupCallEventHandler, "getGroupCallById").mockReturnValue(groupCall);
+            jest.spyOn(client.groupCallEventHandler!, "getGroupCallById").mockReturnValue(groupCall);
             // @ts-ignore Mock onIncomingCall is private
             jest.spyOn(groupCall, "onIncomingCall");
 
diff --git a/spec/unit/webrtc/groupCall.spec.ts b/spec/unit/webrtc/groupCall.spec.ts
index 0c0990aa1..e3c850c70 100644
--- a/spec/unit/webrtc/groupCall.spec.ts
+++ b/spec/unit/webrtc/groupCall.spec.ts
@@ -939,7 +939,7 @@ describe('Group Call', function() {
             groupCall.leave();
 
             const call = new MockCall(room.roomId, groupCall.groupCallId);
-            mockClient.callEventHandler.calls = new Map<string, MatrixCall>([
+            mockClient.callEventHandler!.calls = new Map<string, MatrixCall>([
                 [call.callId, call.typed()],
             ]);
             await groupCall.enter();
diff --git a/spec/unit/webrtc/groupCallEventHandler.spec.ts b/spec/unit/webrtc/groupCallEventHandler.spec.ts
index e948f8afa..6712b0f09 100644
--- a/spec/unit/webrtc/groupCallEventHandler.spec.ts
+++ b/spec/unit/webrtc/groupCallEventHandler.spec.ts
@@ -74,7 +74,7 @@ describe('Group Call Event Handler', function() {
                 { roomId: FAKE_ROOM_ID } as unknown as RoomState,
             );
 
-            const groupCall = groupCallEventHandler.groupCalls.get(FAKE_ROOM_ID);
+            const groupCall = groupCallEventHandler.groupCalls.get(FAKE_ROOM_ID)!;
 
             expect(groupCall.state).toBe(GroupCallState.LocalCallFeedUninitialized);
 
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 3e9950a43..6e43b48be 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -2462,7 +2462,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
             this.emit(CallEvent.Hangup, this);
         }
 
-        this.client.callEventHandler.calls.delete(this.callId);
+        this.client.callEventHandler!.calls.delete(this.callId);
     }
 
     private stopAllMedia(): void {
@@ -2670,7 +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()) ?? undefined;
+        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 7c2be58ff..93035e624 100644
--- a/src/webrtc/callEventHandler.ts
+++ b/src/webrtc/callEventHandler.ts
@@ -183,11 +183,11 @@ export class CallEventHandler {
         const content = event.getContent();
         const callRoomId = (
             event.getRoomId() ||
-            this.client.groupCallEventHandler.getGroupCallById(content.conf_id)?.room?.roomId
+            this.client.groupCallEventHandler!.getGroupCallById(content.conf_id)?.room?.roomId
         );
         const groupCallId = content.conf_id;
         const type = event.getType() as EventType;
-        const senderId = event.getSender();
+        const senderId = event.getSender()!;
         const weSentTheEvent = senderId === this.client.credentials.userId;
         let call = content.call_id ? this.calls.get(content.call_id) : undefined;
         //console.info("RECV %s content=%s", type, JSON.stringify(content));
@@ -196,7 +196,7 @@ export class CallEventHandler {
 
         let groupCall: GroupCall | undefined;
         if (groupCallId) {
-            groupCall = this.client.groupCallEventHandler.getGroupCallById(groupCallId);
+            groupCall = this.client.groupCallEventHandler!.getGroupCallById(groupCallId);
 
             if (!groupCall) {
                 logger.warn(`Cannot find a group call ${groupCallId} for event ${type}. Ignoring event.`);
diff --git a/src/webrtc/groupCall.ts b/src/webrtc/groupCall.ts
index 150b71ea3..c2fd3c4fb 100644
--- a/src/webrtc/groupCall.ts
+++ b/src/webrtc/groupCall.ts
@@ -207,7 +207,7 @@ export class GroupCall extends TypedEventEmitter<
     }
 
     public async create() {
-        this.client.groupCallEventHandler.groupCalls.set(this.room.roomId, this);
+        this.client.groupCallEventHandler!.groupCalls.set(this.room.roomId, this);
 
         await this.client.sendStateEvent(
             this.room.roomId,
@@ -324,7 +324,7 @@ export class GroupCall extends TypedEventEmitter<
 
         this.client.on(CallEventHandlerEvent.Incoming, this.onIncomingCall);
 
-        const calls = this.client.callEventHandler.calls.values();
+        const calls = this.client.callEventHandler!.calls.values();
 
         for (const call of calls) {
             this.onIncomingCall(call);
@@ -406,7 +406,7 @@ export class GroupCall extends TypedEventEmitter<
         }
 
         this.participants = [];
-        this.client.groupCallEventHandler.groupCalls.delete(this.room.roomId);
+        this.client.groupCallEventHandler!.groupCalls.delete(this.room.roomId);
 
         if (emitStateEvent) {
             const existingStateEvent = this.room.currentState.getStateEvents(
@@ -699,7 +699,7 @@ export class GroupCall extends TypedEventEmitter<
             "m.call_id": this.groupCallId,
             "m.devices": [
                 {
-                    "device_id": this.client.getDeviceId(),
+                    "device_id": this.client.getDeviceId()!,
                     "session_id": this.client.getSessionId(),
                     "feeds": this.getLocalFeeds().map((feed) => ({
                         purpose: feed.purpose,
diff --git a/src/webrtc/mediaHandler.ts b/src/webrtc/mediaHandler.ts
index a07016bf6..3cea257ca 100644
--- a/src/webrtc/mediaHandler.ts
+++ b/src/webrtc/mediaHandler.ts
@@ -123,7 +123,7 @@ export class MediaHandler extends TypedEventEmitter<
         this.userMediaStreams = [];
         this.localUserMediaStream = undefined;
 
-        for (const call of this.client.callEventHandler.calls.values()) {
+        for (const call of this.client.callEventHandler!.calls.values()) {
             if (call.callHasEnded() || !callMediaStreamParams.has(call.callId)) {
                 continue;
             }
@@ -140,7 +140,7 @@ export class MediaHandler extends TypedEventEmitter<
             await call.updateLocalUsermediaStream(stream);
         }
 
-        for (const groupCall of this.client.groupCallEventHandler.groupCalls.values()) {
+        for (const groupCall of this.client.groupCallEventHandler!.groupCalls.values()) {
             if (!groupCall.localCallFeed) {
                 continue;
             }
diff --git a/tsconfig.json b/tsconfig.json
index 69c3f0196..9776cfbab 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -8,6 +8,7 @@
     "noImplicitAny": false,
     "noUnusedLocals": true,
     "noEmit": true,
+    "strict": true,
     "declaration": true
   },
   "include": [