diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index bc1c18023..e7487311c 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -1916,6 +1916,8 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
         should_delete_params = ()
         if not delete_local_events:
             should_delete_expr += " AND event_id NOT LIKE ?"
+
+            # We include the parameter twice since we use the expression twice
             should_delete_params += (
                 "%:" + self.hs.hostname,
                 "%:" + self.hs.hostname,