diff --git a/src/room/GroupCallView.test.tsx b/src/room/GroupCallView.test.tsx
index 712b6d98..87e93499 100644
--- a/src/room/GroupCallView.test.tsx
+++ b/src/room/GroupCallView.test.tsx
@@ -118,6 +118,7 @@ function createGroupCallView(widget: WidgetHelpers | null): {
         skipLobby={false}
         hideHeader={true}
         rtcSession={rtcSession as unknown as MatrixRTCSession}
+        isJoined
         muteStates={muteState}
         widget={widget}
       />
diff --git a/src/room/GroupCallView.tsx b/src/room/GroupCallView.tsx
index ee1208c2..6203c675 100644
--- a/src/room/GroupCallView.tsx
+++ b/src/room/GroupCallView.tsx
@@ -46,7 +46,6 @@ import {
 } from "../livekit/MediaDevicesContext";
 import { useMatrixRTCSessionMemberships } from "../useMatrixRTCSessionMemberships";
 import { enterRTCSession, leaveRTCSession } from "../rtcSessionHelpers";
-import { useMatrixRTCSessionJoinState } from "../useMatrixRTCSessionJoinState";
 import { useRoomEncryptionSystem } from "../e2ee/sharedKeyManagement";
 import { useRoomAvatar } from "./useRoomAvatar";
 import { useRoomName } from "./useRoomName";
@@ -74,6 +73,7 @@ interface Props {
   skipLobby: boolean;
   hideHeader: boolean;
   rtcSession: MatrixRTCSession;
+  isJoined: boolean;
   muteStates: MuteStates;
   widget: WidgetHelpers | null;
 }
@@ -86,11 +86,11 @@ export const GroupCallView: FC<Props> = ({
   skipLobby,
   hideHeader,
   rtcSession,
+  isJoined,
   muteStates,
   widget,
 }) => {
   const memberships = useMatrixRTCSessionMemberships(rtcSession);
-  const isJoined = useMatrixRTCSessionJoinState(rtcSession);
   const leaveSoundContext = useLatest(
     useAudioContext({
       sounds: callEventAudioSounds,
diff --git a/src/room/MuteStates.test.tsx b/src/room/MuteStates.test.tsx
index 99f7eaf8..0d21df3b 100644
--- a/src/room/MuteStates.test.tsx
+++ b/src/room/MuteStates.test.tsx
@@ -6,7 +6,7 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { afterAll, afterEach, describe, expect, it, vi } from "vitest";
-import { type FC, useCallback, useState, type ReactNode } from "react";
+import { type FC, useCallback, useState } from "react";
 import { render, screen } from "@testing-library/react";
 import { MemoryRouter } from "react-router-dom";
 import userEvent from "@testing-library/user-event";
@@ -20,8 +20,12 @@ import {
 } from "../livekit/MediaDevicesContext";
 import { mockConfig } from "../utils/test";
 
-function TestComponent(): ReactNode {
-  const muteStates = useMuteStates();
+interface TestComponentProps {
+  isJoined?: boolean;
+}
+
+const TestComponent: FC<TestComponentProps> = ({ isJoined = false }) => {
+  const muteStates = useMuteStates(isJoined);
   const onToggleAudio = useCallback(
     () => muteStates.audio.setEnabled?.(!muteStates.audio.enabled),
     [muteStates],
@@ -37,7 +41,7 @@ function TestComponent(): ReactNode {
       </div>
     </div>
   );
-}
+};
 
 const mockMicrophone: MediaDeviceInfo = {
   deviceId: "",
@@ -134,7 +138,7 @@ describe("useMuteStates", () => {
     expect(screen.getByTestId("video-enabled").textContent).toBe("false");
   });
 
-  it("should be enabled by default", () => {
+  it("enables devices by default in the lobby", () => {
     mockConfig();
 
     render(
@@ -148,6 +152,22 @@ describe("useMuteStates", () => {
     expect(screen.getByTestId("video-enabled").textContent).toBe("true");
   });
 
+  it("disables devices by default in the call", () => {
+    // Disabling new devices in the call ensures that connecting a webcam
+    // mid-call won't cause it to suddenly be enabled without user input
+    mockConfig();
+
+    render(
+      <MemoryRouter>
+        <MediaDevicesContext.Provider value={mockMediaDevices()}>
+          <TestComponent isJoined />
+        </MediaDevicesContext.Provider>
+      </MemoryRouter>,
+    );
+    expect(screen.getByTestId("audio-enabled").textContent).toBe("false");
+    expect(screen.getByTestId("video-enabled").textContent).toBe("false");
+  });
+
   it("uses defaults from config", () => {
     mockConfig({
       media_devices: {
diff --git a/src/room/MuteStates.ts b/src/room/MuteStates.ts
index 13227378..90557bf9 100644
--- a/src/room/MuteStates.ts
+++ b/src/room/MuteStates.ts
@@ -74,17 +74,17 @@ function useMuteState(
   );
 }
 
-export function useMuteStates(): MuteStates {
+export function useMuteStates(isJoined: boolean): MuteStates {
   const devices = useMediaDevices();
 
   const { skipLobby } = useUrlParams();
 
   const audio = useMuteState(devices.audioInput, () => {
-    return Config.get().media_devices.enable_audio && !skipLobby;
+    return Config.get().media_devices.enable_audio && !skipLobby && !isJoined;
   });
   const video = useMuteState(
     devices.videoInput,
-    () => Config.get().media_devices.enable_video && !skipLobby,
+    () => Config.get().media_devices.enable_video && !skipLobby && !isJoined,
   );
 
   useEffect(() => {
diff --git a/src/room/RoomPage.tsx b/src/room/RoomPage.tsx
index dcebf44b..b52e5f1f 100644
--- a/src/room/RoomPage.tsx
+++ b/src/room/RoomPage.tsx
@@ -40,6 +40,7 @@ import { useOptInAnalytics } from "../settings/settings";
 import { Config } from "../config/Config";
 import { Link } from "../button/Link";
 import { ErrorView } from "../ErrorView";
+import { useMatrixRTCSessionJoinState } from "../useMatrixRTCSessionJoinState";
 
 export const RoomPage: FC = () => {
   const {
@@ -66,7 +67,10 @@ export const RoomPage: FC = () => {
   const { avatarUrl, displayName: userDisplayName } = useProfile(client);
 
   const groupCallState = useLoadGroupCall(client, roomIdOrAlias, viaServers);
-  const muteStates = useMuteStates();
+  const isJoined = useMatrixRTCSessionJoinState(
+    groupCallState.kind === "loaded" ? groupCallState.rtcSession : undefined,
+  );
+  const muteStates = useMuteStates(isJoined);
 
   useEffect(() => {
     // If we've finished loading, are not already authed and we've been given a display name as
@@ -111,6 +115,7 @@ export const RoomPage: FC = () => {
             widget={widget}
             client={client!}
             rtcSession={groupCallState.rtcSession}
+            isJoined={isJoined}
             isPasswordlessUser={passwordlessUser}
             confineToRoom={confineToRoom}
             preload={preload}
diff --git a/src/useMatrixRTCSessionJoinState.ts b/src/useMatrixRTCSessionJoinState.ts
index 0bdaa25d..eac94d63 100644
--- a/src/useMatrixRTCSessionJoinState.ts
+++ b/src/useMatrixRTCSessionJoinState.ts
@@ -10,35 +10,33 @@ import {
   type MatrixRTCSession,
   MatrixRTCSessionEvent,
 } from "matrix-js-sdk/src/matrixrtc/MatrixRTCSession";
-import { useCallback, useEffect, useState } from "react";
+import { useEffect, useState } from "react";
 
 export function useMatrixRTCSessionJoinState(
-  rtcSession: MatrixRTCSession,
+  rtcSession: MatrixRTCSession | undefined,
 ): boolean {
-  const [isJoined, setJoined] = useState(rtcSession.isJoined());
-
-  const onJoinStateChanged = useCallback(
-    (isJoined: boolean) => {
-      logger.info(
-        `Session in room ${rtcSession.room.roomId} changed to ${
-          isJoined ? "joined" : "left"
-        }`,
-      );
-      setJoined(isJoined);
-    },
-    [rtcSession],
-  );
+  const [, setNumUpdates] = useState(0);
 
   useEffect(() => {
-    rtcSession.on(MatrixRTCSessionEvent.JoinStateChanged, onJoinStateChanged);
+    if (rtcSession !== undefined) {
+      const onJoinStateChanged = (isJoined: boolean): void => {
+        logger.info(
+          `Session in room ${rtcSession.room.roomId} changed to ${
+            isJoined ? "joined" : "left"
+          }`,
+        );
+        setNumUpdates((n) => n + 1); // Force an update
+      };
+      rtcSession.on(MatrixRTCSessionEvent.JoinStateChanged, onJoinStateChanged);
 
-    return (): void => {
-      rtcSession.off(
-        MatrixRTCSessionEvent.JoinStateChanged,
-        onJoinStateChanged,
-      );
-    };
-  }, [rtcSession, onJoinStateChanged]);
+      return (): void => {
+        rtcSession.off(
+          MatrixRTCSessionEvent.JoinStateChanged,
+          onJoinStateChanged,
+        );
+      };
+    }
+  }, [rtcSession]);
 
-  return isJoined;
+  return rtcSession?.isJoined() ?? false;
 }