1 files changed, 3 insertions, 1 deletions
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 174a743f6a..fa3e9acc74 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -1689,7 +1689,9 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         #
         # the prev_events consist solely of the previous membership event.
         prev_event_ids = [previous_membership_event.event_id]
-        auth_event_ids = previous_membership_event.auth_event_ids() + prev_event_ids
+        auth_event_ids = (
+            list(previous_membership_event.auth_event_ids()) + prev_event_ids
+        )
 
         event, context = await self.event_creation_handler.create_event(
             requester,