diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 9d528d1e5b..1384aa0d81 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -264,6 +264,7 @@ class E2eKeysHandler(object):
 
         return ret
 
+    @defer.inlineCallbacks
     def get_cross_signing_keys_from_cache(self, query, from_user_id):
         """Get cross-signing keys for users from the database