diff --git a/src/backend/services/socket/SocketService.test.ts b/src/backend/services/socket/SocketService.test.ts
index 127e6b9dd..a8172d928 100644
--- a/src/backend/services/socket/SocketService.test.ts
+++ b/src/backend/services/socket/SocketService.test.ts
@@ -625,6 +625,24 @@ describe('SocketService (live socket.io)', () => {
             await closeAll(userId, [other]);
         });
 
+        it('joins only the ack room of the room it is asked in', async () => {
+            const userId = await userIdOf();
+            const socket = await connect({
+                auth_token: user.token,
+                acks: ['demo.ack'],
+            });
+
+            expect(
+                socketService.has({ room: ackRoom(String(userId), 'demo.ack') }),
+            ).toBe(true);
+            for (const room of [accountSocketRoom(userId), socket.id!]) {
+                expect(
+                    socketService.has({ room: ackRoom(room, 'demo.ack') }),
+                ).toBe(false);
+            }
+            await closeAll(userId, [socket]);
+        });
+
         it('hears nothing from a room nobody is in', async () => {
             await expect(
                 socketService.askWithAck(
diff --git a/src/backend/services/socket/SocketService.ts b/src/backend/services/socket/SocketService.ts
index 442d95555..9907e61ae 100644
--- a/src/backend/services/socket/SocketService.ts
+++ b/src/backend/services/socket/SocketService.ts
@@ -681,13 +681,11 @@ export class SocketService extends PuterService {
                 // user.id is numeric in the DB; stringify for room name
                 // so adapter lookups key on a stable type.
                 const rooms = socketRoomsFor(decision.accept);
-                const acks = handshakeAcks(handshakeAuth?.acks);
+                // Asks go to the user's or the app's room, never the others.
                 socket.join([
                     ...rooms,
-                    ...acks.flatMap((event) =>
-                        [...rooms, socket.id].map((room) =>
-                            ackRoom(room, event),
-                        ),
+                    ...handshakeAcks(handshakeAuth?.acks).map((event) =>
+                        ackRoom(rooms[0], event),
                     ),
                 ]);
                 next();