1 files changed, 1 insertions, 1 deletions
diff --git a/synapse/storage/databases/main/signatures.py b/synapse/storage/databases/main/signatures.py
index 0518b8b910..95148fd227 100644
--- a/synapse/storage/databases/main/signatures.py
+++ b/synapse/storage/databases/main/signatures.py
@@ -26,7 +26,7 @@ from synapse.util.caches.descriptors import cached, cachedList
 
 class SignatureWorkerStore(EventsWorkerStore):
     @cached()
-    def get_event_reference_hash(self, event_id):
+    def get_event_reference_hash(self, event_id: str) -> Dict[str, Dict[str, bytes]]:
         # This is a dummy function to allow get_event_reference_hashes
         # to use its cache
         raise NotImplementedError()