diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index 94bd5347a..a9c76f323 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -207,12 +207,12 @@ class ProfileHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def set_displayname(self, target_user, requester, new_displayname, by_admin=False):
-        """target_user is the user whose displayname is to be changed;
-        requester is the user attempting to make this change."""
+        """target_user is the UserID whose displayname is to be changed;
+        requester is the authenticated user attempting to make this change."""
         if not self.hs.is_mine(target_user):
             raise SynapseError(400, "User is not hosted on this Home Server")
 
-        if not by_admin and target_user != requester.user:
+        if not by_admin and requester and target_user != requester.user:
             raise AuthError(400, "Cannot set another user's displayname")
 
         if not by_admin and self.hs.config.disable_set_displayname:
@@ -239,7 +239,8 @@ class ProfileHandler(BaseHandler):
                 target_user.to_string(), profile
             )
 
-        yield self._update_join_states(requester, target_user)
+        if requester:
+            yield self._update_join_states(requester, target_user)
 
         # start a profile replication push
         run_in_background(self._replicate_profiles)
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 14031cea4..e308fcbb4 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -178,7 +178,7 @@ class RegistrationHandler(BaseHandler):
 
             if display_name:
                 yield self.profile_handler.set_displayname(
-                    user, user, display_name, by_admin=True,
+                    user, None, display_name, by_admin=True,
                 )
 
             if self.hs.config.user_directory_search_all_users:
@@ -208,7 +208,7 @@ class RegistrationHandler(BaseHandler):
                     )
 
                     yield self.profile_handler.set_displayname(
-                        user, user, user.localpart, by_admin=True,
+                        user, None, user.localpart, by_admin=True,
                     )
 
                 except SynapseError:
@@ -257,7 +257,7 @@ class RegistrationHandler(BaseHandler):
         )
 
         yield self.profile_handler.set_displayname(
-            user, user, user.localpart, by_admin=True,
+            user, None, user.localpart, by_admin=True,
         )
 
         defer.returnValue(user_id)
@@ -308,7 +308,7 @@ class RegistrationHandler(BaseHandler):
             )
 
             yield self.profile_handler.set_displayname(
-                user, user, user.localpart, by_admin=True,
+                user, None, user.localpart, by_admin=True,
             )
         except Exception as e:
             yield self.store.add_access_token_to_user(user_id, token)
@@ -466,7 +466,7 @@ class RegistrationHandler(BaseHandler):
             )
             if displayname is not None:
                 yield self.profile_handler.set_displayname(
-                    user, user, displayname, by_admin=True,
+                    user, None, displayname, by_admin=True,
                 )
         else:
             yield self._auth_handler.delete_access_tokens_for_user(user_id)