diff --git a/synapse/storage/schema/delta/30/public_rooms.sql b/synapse/storage/schema/delta/30/public_rooms.sql
index 3400898ed..f09db4faa 100644
--- a/synapse/storage/schema/delta/30/public_rooms.sql
+++ b/synapse/storage/schema/delta/30/public_rooms.sql
@@ -15,7 +15,9 @@
 
 
 /* This release removes the restriction that published rooms must have an alias,
- * so we go back and ensure the only 'public' rooms are ones with an alias.*/
+ * so we go back and ensure the only 'public' rooms are ones with an alias.
+ * We use (1 = 0) and (1 = 1) so that it works in both postgres and sqlite
+ */
 UPDATE rooms SET is_public = (1 = 0) WHERE is_public = (1 = 1) AND room_id not in (
     SELECT room_id FROM room_aliases
 );