diff --git a/synapse/replication/http/registration.py b/synapse/replication/http/registration.py
index 5030bde499..513dafab39 100644
--- a/synapse/replication/http/registration.py
+++ b/synapse/replication/http/registration.py
@@ -17,12 +17,7 @@ import logging
 
 from twisted.internet import defer
 
-from synapse.events import event_type_from_format_version
-from synapse.events.snapshot import EventContext
-from synapse.http.servlet import parse_json_object_from_request
 from synapse.replication.http._base import ReplicationEndpoint
-from synapse.types import Requester, UserID
-from synapse.util.metrics import Measure
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index 5ca9421a07..9f750f7cf5 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -481,7 +481,7 @@ class RegisterRestServlet(RestServlet):
         )
 
         if self.hs.config.worker_app:
-            self._invalidate_caches_client(registered_user_id)
+            self._invalidate_caches_client(user_id)
 
         defer.returnValue((yield self._create_registration_details(user_id, body)))