diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index 53cc29becb..6fe53f70e5 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -490,7 +490,7 @@ class RoomMembershipRestServlet(ClientV1RestServlet):
         )
 
         if membership_action == "forget":
-            self.handlers.room_member_handler.forget(user, room_id)
+            yield self.handlers.room_member_handler.forget(user, room_id)
 
         defer.returnValue((200, {}))