diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index b6010bb41..b8e1af580 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -341,9 +341,9 @@ class RoomMemberHandler(object):
         prev_events_and_hashes = yield self.store.get_prev_events_for_room(
             room_id,
         )
-        latest_event_ids = [
+        latest_event_ids = (
             event_id for (event_id, _, _) in prev_events_and_hashes
-        ]
+        )
 
         current_state_ids = yield self.state_handler.get_current_state_ids(
             room_id, latest_event_ids=latest_event_ids,