diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index ed7d936b3..1160b98cc 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -584,7 +584,7 @@ class RoomMemberWorkerStore(EventsWorkerStore):
 
     @cached(max_entries=10000)
     def _get_joined_profile_from_event_id(self, event_id):
-        raise NotADirectoryError()
+        raise NotImplementedError()
 
     @cachedList(
         cached_method_name="_get_joined_profile_from_event_id",