diff --git a/synapse/storage/registration.py b/synapse/storage/registration.py
index 86fd2600f..8a63fe469 100644
--- a/synapse/storage/registration.py
+++ b/synapse/storage/registration.py
@@ -39,7 +39,7 @@ class RegistrationStore(SQLBaseStore):
         """
         next_id = yield self._access_tokens_id_gen.get_next()
 
-        self._simple_insert(
+        yield self._simple_insert(
             "access_tokens",
             {
                 "id": next_id,