diff --git a/synapse/util/distributor.py b/synapse/util/distributor.py
index 194da8763..e14c8bdfd 100644
--- a/synapse/util/distributor.py
+++ b/synapse/util/distributor.py
@@ -27,6 +27,7 @@ def user_left_room(distributor, user, room_id):
     distributor.fire("user_left_room", user=user, room_id=room_id)
 
 
+# XXX: this is no longer used. We should probably kill it.
 def user_joined_room(distributor, user, room_id):
     distributor.fire("user_joined_room", user=user, room_id=room_id)