diff --git a/synapse/storage/event_federation.py b/synapse/storage/event_federation.py
index 03942fec7..a3da11779 100644
--- a/synapse/storage/event_federation.py
+++ b/synapse/storage/event_federation.py
@@ -411,7 +411,8 @@ class EventFederationStore(SQLBaseStore):
             )
 
             for row in txn.fetchall():
-                queue.put((-row[0], row[1]))
+                if row[1] not in event_results:
+                    queue.put((-row[0], row[1]))
 
         return event_results