1 files changed, 16 insertions, 6 deletions
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index be120b2f34..ef8753b1ff 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -326,13 +326,23 @@ class DeviceHandler(BaseHandler):
                         possibly_changed.add(state_key)
                         break
 
-        users_who_share_room = yield self.store.get_users_who_share_room_with_user(
-            user_id
-        )
+        if possibly_changed:
+            users_who_share_room = yield self.store.get_users_who_share_room_with_user(
+                user_id
+            )
 
-        # Take the intersection of the users whose devices may have changed
-        # and those that actually still share a room with the user
-        defer.returnValue(users_who_share_room & possibly_changed)
+            # Take the intersection of the users whose devices may have changed
+            # and those that actually still share a room with the user
+            possibly_joined = possibly_changed & users_who_share_room
+            possibly_left = possibly_changed - users_who_share_room
+        else:
+            possibly_joined = []
+            possibly_left = []
+
+        defer.returnValue({
+            "changed": list(possibly_joined),
+            "left": list(possibly_left),
+        })
 
     @defer.inlineCallbacks
     def on_federation_query_user_devices(self, user_id):