diff --git a/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go b/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go
index f8677eb4e..6e31743b4 100644
--- a/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go
+++ b/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go
@@ -42,5 +42,11 @@ func UpDropEventReferenceSHAPrevEvents(ctx context.Context, tx *sql.Tx) error {
 	if err != nil {
 		return fmt.Errorf("failed to execute upgrade: %w", err)
 	}
+	// re-add constraint, as it seems to be dropped as well
+	_, err = tx.ExecContext(ctx, `ALTER TABLE roomserver_previous_events ADD CONSTRAINT roomserver_previous_event_id_unique UNIQUE (previous_event_id);`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+
+	}
 	return nil
 }