diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 3142d85788..1711d5ac5c 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -397,7 +397,6 @@ class RegistrationHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def _join_user_to_room(self, requester, room_identifier):
-        room_id = None
         room_member_handler = self.hs.get_room_member_handler()
         if RoomID.is_valid(room_identifier):
             room_id = room_identifier