diff --git a/package.json b/package.json
index 89dc3c3aafe..2b67e929dee 100644
--- a/package.json
+++ b/package.json
@@ -122,7 +122,7 @@
         "typedoc-plugin-coverage": "^3.0.0",
         "typedoc-plugin-mdn-links": "^3.0.3",
         "typedoc-plugin-missing-exports": "^3.0.0",
-        "typescript": "^5.3.3"
+        "typescript": "^5.4.2"
     },
     "@casualbot/jest-sonar-reporter": {
         "outputDirectory": "coverage",
diff --git a/spec/test-utils/beacon.ts b/spec/test-utils/beacon.ts
index 9cfebf95675..08771379af1 100644
--- a/spec/test-utils/beacon.ts
+++ b/spec/test-utils/beacon.ts
@@ -101,9 +101,8 @@ export const makeGeolocationPosition = ({
 }: {
     timestamp?: number;
     coords: Partial<GeolocationCoordinates>;
-}): GeolocationPosition => ({
-    timestamp: timestamp ?? 1647256791840,
-    coords: {
+}): GeolocationPosition => {
+    const { toJSON, ...coordsJSON } = {
         accuracy: 1,
         latitude: 54.001927,
         longitude: -8.253491,
@@ -112,5 +111,16 @@ export const makeGeolocationPosition = ({
         heading: null,
         speed: null,
         ...coords,
-    },
-});
+    };
+    const posJSON = {
+        timestamp: timestamp ?? 1647256791840,
+        coords: {
+            toJSON: () => coordsJSON,
+            ...coordsJSON,
+        },
+    };
+    return {
+        toJSON: () => posJSON,
+        ...posJSON,
+    };
+};
diff --git a/spec/test-utils/webrtc.ts b/spec/test-utils/webrtc.ts
index 9b91a3d272b..519701bdaa9 100644
--- a/spec/test-utils/webrtc.ts
+++ b/spec/test-utils/webrtc.ts
@@ -147,10 +147,13 @@ export class MockRTCPeerConnection {
     }
 
     constructor() {
-        this.localDescription = {
+        const localDescriptionJSON = {
             sdp: DUMMY_SDP,
-            type: "offer",
-            toJSON: function () {},
+            type: "offer" as RTCSdpType,
+        };
+        this.localDescription = {
+            toJSON: () => localDescriptionJSON,
+            ...localDescriptionJSON,
         };
 
         this.readyToNegotiate = new Promise<void>((resolve) => {
@@ -265,7 +268,7 @@ export class MockRTCRtpTransceiver {
         this.peerConn.needsNegotiation = true;
     }
 
-    public setCodecPreferences = jest.fn<void, RTCRtpCodecCapability[]>();
+    public setCodecPreferences = jest.fn<void, RTCRtpCodec[]>();
 }
 
 export class MockMediaStreamTrack {
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 6a8a15e0612..c2b24cadb82 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -2024,7 +2024,7 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
                 this.sendVoipEvent(EventType.CallNegotiate, {
                     lifetime: CALL_TIMEOUT_MS,
-                    description: this.peerConn!.localDescription?.toJSON(),
+                    description: this.peerConn!.localDescription?.toJSON() as RTCSessionDescription,
                     [SDPStreamMetadataKey]: this.getLocalSDPStreamMetadata(true),
                 });
             }
@@ -2152,9 +2152,9 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
 
         // clunky because TypeScript can't follow the types through if we use an expression as the key
         if (this.state === CallState.CreateOffer) {
-            content.offer = this.peerConn!.localDescription?.toJSON();
+            content.offer = this.peerConn!.localDescription?.toJSON() as RTCSessionDescription;
         } else {
-            content.description = this.peerConn!.localDescription?.toJSON();
+            content.description = this.peerConn!.localDescription?.toJSON() as RTCSessionDescription;
         }
 
         content.capabilities = {
diff --git a/yarn.lock b/yarn.lock
index 82fc43f285f..33c80fb2509 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -6378,10 +6378,10 @@ typedoc@^0.26.0:
     shiki "^1.16.2"
     yaml "^2.5.1"
 
-typescript@^5.3.3:
-  version "5.5.4"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-5.5.4.tgz#d9852d6c82bad2d2eda4fd74a5762a8f5909e9ba"
-  integrity sha512-Mtq29sKDAEYP7aljRgtPOpTvOfbwRWlS6dPRzwjdE+C0R4brX/GUyhHSecbHMFLNBLcJIPt9nl9yG5TZ1weH+Q==
+typescript@^5.4.2:
+  version "5.6.2"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-5.6.2.tgz#d1de67b6bef77c41823f822df8f0b3bcff60a5a0"
+  integrity sha512-NW8ByodCSNCwZeghjN3o+JX5OFH0Ojg6sadjEKY4huZ52TqbJTJnDo5+Tw98lSy63NZvi4n+ez5m2u5d4PkZyw==
 
 uc.micro@^2.0.0, uc.micro@^2.1.0:
   version "2.1.0"