diff --git a/src/@types/global.d.ts b/src/@types/global.d.ts
index c7e65ff77..679a6afba 100644
--- a/src/@types/global.d.ts
+++ b/src/@types/global.d.ts
@@ -23,6 +23,7 @@ declare global {
     // use `number` as the return type in all cases for global.set{Interval,Timeout},
     // so we don't accidentally use the methods on NodeJS.Timeout - they only exist in a subset of environments.
     // The overload for clear{Interval,Timeout} is resolved as expected.
+    // We use `ReturnType<typeof setTimeout>` in the code to be agnostic of if this definition gets loaded.
     function setInterval(handler: TimerHandler, timeout: number, ...arguments: any[]): number;
     function setTimeout(handler: TimerHandler, timeout: number, ...arguments: any[]): number;
 
diff --git a/src/client.ts b/src/client.ts
index 78249b121..a705f5df5 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -913,7 +913,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     protected syncLeftRoomsPromise: Promise<Room[]>;
     protected syncedLeftRooms = false;
     protected clientOpts: IStoredClientOpts;
-    protected clientWellKnownIntervalID: number;
+    protected clientWellKnownIntervalID: ReturnType<typeof setInterval>;
     protected canResetTimelineCallback: ResetTimelineCallback;
 
     // The pushprocessor caches useful things, so keep one and re-use it
@@ -931,7 +931,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     protected clientWellKnownPromise: Promise<IClientWellKnown>;
     protected turnServers: ITurnServer[] = [];
     protected turnServersExpiry = 0;
-    protected checkTurnServersIntervalID: number;
+    protected checkTurnServersIntervalID: ReturnType<typeof setInterval>;
     protected exportedOlmDeviceToImport: IOlmDevice;
     protected txnCtr = 0;
     protected mediaHandler = new MediaHandler(this);
diff --git a/src/crypto/DeviceList.ts b/src/crypto/DeviceList.ts
index 40c055c7b..000e79f93 100644
--- a/src/crypto/DeviceList.ts
+++ b/src/crypto/DeviceList.ts
@@ -95,7 +95,7 @@ export class DeviceList extends TypedEventEmitter<EmittedEvents, CryptoEventHand
     // The time the save is scheduled for
     private savePromiseTime: number = null;
     // The timer used to delay the save
-    private saveTimer: number = null;
+    private saveTimer: ReturnType<typeof setTimeout> = null;
     // True if we have fetched data from the server or loaded a non-empty
     // set of device data from the store
     private hasFetched: boolean = null;
diff --git a/src/crypto/OutgoingRoomKeyRequestManager.ts b/src/crypto/OutgoingRoomKeyRequestManager.ts
index 832294110..013a6d08e 100644
--- a/src/crypto/OutgoingRoomKeyRequestManager.ts
+++ b/src/crypto/OutgoingRoomKeyRequestManager.ts
@@ -78,7 +78,7 @@ export enum RoomKeyRequestState {
 export class OutgoingRoomKeyRequestManager {
     // handle for the delayed call to sendOutgoingRoomKeyRequests. Non-null
     // if the callback has been set, or if it is still running.
-    private sendOutgoingRoomKeyRequestsTimer: number = null;
+    private sendOutgoingRoomKeyRequestsTimer: ReturnType<typeof setTimeout> = null;
 
     // sanity check to ensure that we don't end up with two concurrent runs
     // of sendOutgoingRoomKeyRequests
diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index 0842dda53..df18d83a0 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -309,7 +309,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
 
     private oneTimeKeyCount: number;
     private needsNewFallback: boolean;
-    private fallbackCleanup?: number; // setTimeout ID
+    private fallbackCleanup?: ReturnType<typeof setTimeout>;
 
     /**
      * Cryptography bits
diff --git a/src/crypto/recoverykey.ts b/src/crypto/recoverykey.ts
index 5c54e6085..124f6c77b 100644
--- a/src/crypto/recoverykey.ts
+++ b/src/crypto/recoverykey.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import bs58 from 'bs58';
+import * as bs58 from 'bs58';
 
 // picked arbitrarily but to try & avoid clashing with any bitcoin ones
 // (which are also base58 encoded, but bitcoin's involve a lot more hashing)
diff --git a/src/crypto/store/indexeddb-crypto-store-backend.ts b/src/crypto/store/indexeddb-crypto-store-backend.ts
index 8e311a1a2..6666fcf01 100644
--- a/src/crypto/store/indexeddb-crypto-store-backend.ts
+++ b/src/crypto/store/indexeddb-crypto-store-backend.ts
@@ -873,7 +873,7 @@ export class Backend implements CryptoStore {
 
     public doTxn<T>(
         mode: Mode,
-        stores: Iterable<string>,
+        stores: string | string[],
         func: (txn: IDBTransaction) => T,
         log: PrefixedLogger = logger,
     ): Promise<T> {
diff --git a/src/crypto/verification/Base.ts b/src/crypto/verification/Base.ts
index 68e9c96fc..351004990 100644
--- a/src/crypto/verification/Base.ts
+++ b/src/crypto/verification/Base.ts
@@ -55,7 +55,7 @@ export class VerificationBase<
     private cancelled = false;
     private _done = false;
     private promise: Promise<void> = null;
-    private transactionTimeoutTimer: number = null;
+    private transactionTimeoutTimer: ReturnType<typeof setTimeout> = null;
     protected expectedEvent: string;
     private resolve: () => void;
     private reject: (e: Error | MatrixEvent) => void;
diff --git a/src/crypto/verification/request/VerificationRequest.ts b/src/crypto/verification/request/VerificationRequest.ts
index 8af56f354..e8eb5b8d3 100644
--- a/src/crypto/verification/request/VerificationRequest.ts
+++ b/src/crypto/verification/request/VerificationRequest.ts
@@ -95,7 +95,7 @@ export class VerificationRequest<
     private eventsByUs = new Map<string, MatrixEvent>();
     private eventsByThem = new Map<string, MatrixEvent>();
     private _observeOnly = false;
-    private timeoutTimer: number = null;
+    private timeoutTimer: ReturnType<typeof setTimeout> = null;
     private _accepting = false;
     private _declining = false;
     private verifierHasFinished = false;
diff --git a/src/index.ts b/src/index.ts
index faab0fed0..c651438fb 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import request from "request";
+import * as request from "request";
 
 import * as matrixcs from "./matrix";
 import * as utils from "./utils";
diff --git a/src/models/beacon.ts b/src/models/beacon.ts
index caea77327..a4f769458 100644
--- a/src/models/beacon.ts
+++ b/src/models/beacon.ts
@@ -54,7 +54,7 @@ export class Beacon extends TypedEventEmitter<Exclude<BeaconEvent, BeaconEvent.N
     public readonly roomId: string;
     private _beaconInfo: BeaconInfoState;
     private _isLive: boolean;
-    private livenessWatchInterval: number;
+    private livenessWatchInterval: ReturnType<typeof setInterval>;
     private _latestLocationState: BeaconLocationState | undefined;
 
     constructor(
diff --git a/src/store/index.ts b/src/store/index.ts
index c47bd20ad..f71f7c093 100644
--- a/src/store/index.ts
+++ b/src/store/index.ts
@@ -37,6 +37,10 @@ export interface ISavedSync {
 export interface IStore {
     readonly accountData: Record<string, MatrixEvent>; // type : content
 
+    // XXX: The indexeddb store exposes a non-standard emitter for the "degraded" event
+    // for when it falls back to being a memory store due to errors.
+    on?: (event: string, handler: (...args: any[]) => void) => void;
+
     /** @return {Promise<boolean>} whether or not the database was newly created in this session. */
     isNewlyCreated(): Promise<boolean>;
 
@@ -105,7 +109,7 @@ export interface IStore {
     /**
      * No-op.
      * @param {Room} room
-     * @param {integer} limit
+     * @param {number} limit
      * @return {Array}
      */
     scrollback(room: Room, limit: number): MatrixEvent[];
diff --git a/src/sync.ts b/src/sync.ts
index 0791920a9..d3aec0d5c 100644
--- a/src/sync.ts
+++ b/src/sync.ts
@@ -152,7 +152,7 @@ export class SyncApi {
     private syncStateData: ISyncStateData = null; // additional data (eg. error object for failed sync)
     private catchingUp = false;
     private running = false;
-    private keepAliveTimer: number = null;
+    private keepAliveTimer: ReturnType<typeof setTimeout> = null;
     private connectionReturnedDefer: IDeferred<boolean> = null;
     private notifEvents: MatrixEvent[] = []; // accumulator of sync events in the current sync response
     private failedSyncCount = 0; // Number of consecutive failed /sync requests
@@ -1390,7 +1390,7 @@ export class SyncApi {
      * Starts polling the connectivity check endpoint
      * @param {number} delay How long to delay until the first poll.
      *        defaults to a short, randomised interval (to prevent
-     *        tightlooping if /versions succeeds but /sync etc. fail).
+     *        tight-looping if /versions succeeds but /sync etc. fail).
      * @return {promise} which resolves once the connection returns
      */
     private startKeepAlives(delay?: number): Promise<boolean> {
diff --git a/src/utils.ts b/src/utils.ts
index 777531286..4885fb948 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -23,7 +23,7 @@ limitations under the License.
 import unhomoglyph from "unhomoglyph";
 import promiseRetry from "p-retry";
 
-import type NodeCrypto from "crypto";
+import type * as NodeCrypto from "crypto";
 import { MatrixEvent } from ".";
 import { M_TIMESTAMP } from "./@types/location";
 
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index dcc1016a6..d6a574713 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -298,7 +298,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
     // yet, null if we have but they didn't send a party ID.
     private opponentPartyId: string;
     private opponentCaps: CallCapabilities;
-    private inviteTimeout: number;
+    private inviteTimeout: ReturnType<typeof setTimeout>;
 
     // The logic of when & if a call is on hold is nontrivial and explained in is*OnHold
     // This flag represents whether we want the other party to be on hold
@@ -322,7 +322,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
     private remoteSDPStreamMetadata: SDPStreamMetadata;
 
-    private callLengthInterval: number;
+    private callLengthInterval: ReturnType<typeof setInterval>;
     private callLength = 0;
 
     constructor(opts: CallOpts) {
@@ -708,9 +708,9 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
         const statsReport = await this.peerConn.getStats();
         const stats = [];
-        for (const item of statsReport) {
+        statsReport.forEach(item => {
             stats.push(item[1]);
-        }
+        });
 
         return stats;
     }
diff --git a/src/webrtc/callFeed.ts b/src/webrtc/callFeed.ts
index 8f61afaa5..fbe308e53 100644
--- a/src/webrtc/callFeed.ts
+++ b/src/webrtc/callFeed.ts
@@ -69,7 +69,7 @@ export class CallFeed extends TypedEventEmitter<CallFeedEvent, EventHandlerMap>
     private frequencyBinCount: Float32Array;
     private speakingThreshold = SPEAKING_THRESHOLD;
     private speaking = false;
-    private volumeLooperTimeout: number;
+    private volumeLooperTimeout: ReturnType<typeof setTimeout>;
 
     constructor(opts: ICallFeedOpts) {
         super();