diff --git a/synapse/handlers/room_list.py b/synapse/handlers/room_list.py
index f466a64ed..2ee63548c 100644
--- a/synapse/handlers/room_list.py
+++ b/synapse/handlers/room_list.py
@@ -188,7 +188,7 @@ class RoomListHandler(BaseHandler):
 
         # bail if no rooms to work on
         if len(rooms_to_scan) == 0:
-            defer.returnValue([])
+            defer.returnValue({})
 
         # _append_room_entry_to_chunk will append to chunk but will stop if
         # len(chunk) > limit