1 files changed, 4 insertions, 0 deletions
diff --git a/synapse/visibility.py b/synapse/visibility.py
index c810a05907..c4048d2477 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -162,6 +162,10 @@ async def filter_event_for_clients_with_state(
     if event.internal_metadata.is_soft_failed():
         return []
 
+    # Fast path if we don't have any user IDs to check.
+    if not user_ids:
+        return ()
+
     # Make a set for all user IDs that haven't been filtered out by a check.
     allowed_user_ids = set(user_ids)