diff --git a/synapse/storage/event_push_actions.py b/synapse/storage/event_push_actions.py
index 8632b2f936..40bfe754b5 100644
--- a/synapse/storage/event_push_actions.py
+++ b/synapse/storage/event_push_actions.py
@@ -361,12 +361,14 @@ class EventPushActionsStore(SQLBaseStore):
                     before_clause += " "
                 before_clause += "AND epa.highlight = 1"
 
+            # NB. This assumes event_ids are globally unique since
+            # it makes the query easier to index
             sql = (
                 "SELECT epa.event_id, epa.room_id,"
                 " epa.stream_ordering, epa.topological_ordering,"
                 " epa.actions, epa.profile_tag, e.received_ts"
                 " FROM event_push_actions epa, events e"
-                " WHERE epa.room_id = e.room_id AND epa.event_id = e.event_id"
+                " WHERE epa.event_id = e.event_id"
                 " AND epa.user_id = ? %s"
                 " ORDER BY epa.stream_ordering DESC"
                 " LIMIT ?"