diff --git a/synapse/storage/user_directory.py b/synapse/storage/user_directory.py
index 348064436..71b050264 100644
--- a/synapse/storage/user_directory.py
+++ b/synapse/storage/user_directory.py
@@ -204,6 +204,7 @@ class UserDirectoryStore(SQLBaseStore):
         )
 
     def get_current_state_deltas(self, prev_stream_id):
+        prev_stream_id = int(prev_stream_id)
         if not self._curr_state_delta_stream_cache.has_any_entity_changed(prev_stream_id):
             return []