diff --git a/synapse/storage/registration.py b/synapse/storage/registration.py
index 7af0cae6a..bda84a744 100644
--- a/synapse/storage/registration.py
+++ b/synapse/storage/registration.py
@@ -101,6 +101,7 @@ class RegistrationStore(SQLBaseStore):
             make_guest,
             appservice_id
         )
+        self.get_user_by_id.invalidate((user_id,))
         self.is_guest.invalidate((user_id,))
 
     def _register(
@@ -156,6 +157,7 @@ class RegistrationStore(SQLBaseStore):
                 (next_id, user_id, token,)
             )
 
+    @cached()
     def get_user_by_id(self, user_id):
         return self._simple_select_one(
             table="users",
@@ -193,6 +195,7 @@ class RegistrationStore(SQLBaseStore):
         }, {
             'password_hash': password_hash
         })
+        self.get_user_by_id.invalidate((user_id,))
 
     @defer.inlineCallbacks
     def user_delete_access_tokens(self, user_id, except_token_ids=[]):