diff --git a/src/app/hooks/useVoiceChannelFull.ts b/src/app/hooks/useVoiceChannelFull.ts
index 638ae1d67..319169419 100644
--- a/src/app/hooks/useVoiceChannelFull.ts
+++ b/src/app/hooks/useVoiceChannelFull.ts
@@ -5,6 +5,7 @@ import { StateEvent } from '../../types/matrix/room';
 import { VoiceLimitContent } from '../features/common-settings/general/RoomVoiceLimit';
 import { useCallMembers, useCallSession } from './useCall';
 import { useMatrixClient } from './useMatrixClient';
+import { voiceChannelOccupancy } from '../utils/voiceChannelFull';
 
 export type VoiceChannelFull = {
   channelFull: boolean;
@@ -26,9 +27,11 @@ export const useVoiceChannelFull = (room: Room): VoiceChannelFull => {
 
   return useMemo(() => {
     const maxUsers = limitEvent?.getContent<VoiceLimitContent>().max_users ?? 0;
-    // A user already counted in the session is rejoining and should not be blocked.
-    const alreadyMember = callMembers.some((m) => m.sender === mx.getSafeUserId());
-    const channelFull = maxUsers > 0 && !alreadyMember && callMembers.length >= maxUsers;
-    return { channelFull, current: callMembers.length, max: maxUsers };
+    // Distinct people, not per-device memberships (Gitea #342).
+    return voiceChannelOccupancy(
+      callMembers.map((m) => m.sender),
+      mx.getSafeUserId(),
+      maxUsers,
+    );
   }, [limitEvent, callMembers, mx]);
 };
diff --git a/src/app/utils/voiceChannelFull.test.ts b/src/app/utils/voiceChannelFull.test.ts
new file mode 100644
index 000000000..75cca8a98
--- /dev/null
+++ b/src/app/utils/voiceChannelFull.test.ts
@@ -0,0 +1,28 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { voiceChannelOccupancy } from './voiceChannelFull';
+
+test('voiceChannelOccupancy: one user on two devices fills one slot, not two', () => {
+  assert.deepEqual(voiceChannelOccupancy(['@a:x', '@a:x'], '@b:x', 2), {
+    channelFull: false,
+    current: 1,
+    max: 2,
+  });
+});
+
+test('voiceChannelOccupancy: full when distinct users reach the limit', () => {
+  assert.deepEqual(voiceChannelOccupancy(['@a:x', '@c:x', '@a:x'], '@b:x', 2), {
+    channelFull: true,
+    current: 2,
+    max: 2,
+  });
+});
+
+test('voiceChannelOccupancy: someone already in the call can always join another device', () => {
+  assert.equal(voiceChannelOccupancy(['@a:x', '@b:x'], '@b:x', 2).channelFull, false);
+});
+
+test('voiceChannelOccupancy: no limit (0) is never full; unknown senders are ignored', () => {
+  assert.equal(voiceChannelOccupancy(['@a:x', '@c:x'], '@b:x', 0).channelFull, false);
+  assert.equal(voiceChannelOccupancy([undefined, '@a:x'], '@b:x', 2).current, 1);
+});
diff --git a/src/app/utils/voiceChannelFull.ts b/src/app/utils/voiceChannelFull.ts
new file mode 100644
index 000000000..ef746195a
--- /dev/null
+++ b/src/app/utils/voiceChannelFull.ts
@@ -0,0 +1,25 @@
+/**
+ * [Gitea #342] Whether a voice channel with an `io.lotus.voice_limit` is full.
+ * Counts distinct PEOPLE, not call memberships: a MatrixRTC membership is per
+ * device, so one user on desktop + phone (or with a crashed tab's membership
+ * not yet expired) used to fill two slots. This matches the server-side guard
+ * (matrix `voice-limit-guard.py`, which reduces LiveKit identities to users).
+ */
+export type VoiceChannelOccupancy = {
+  channelFull: boolean;
+  /** Distinct users in the call. */
+  current: number;
+  max: number;
+};
+
+export const voiceChannelOccupancy = (
+  memberSenders: Array<string | undefined>,
+  myUserId: string,
+  maxUsers: number,
+): VoiceChannelOccupancy => {
+  const users = new Set(memberSenders.filter((s): s is string => !!s));
+  // A user already in the call (another device, or rejoining) is never blocked.
+  const alreadyMember = users.has(myUserId);
+  const channelFull = maxUsers > 0 && !alreadyMember && users.size >= maxUsers;
+  return { channelFull, current: users.size, max: maxUsers };
+};