diff --git a/kernel/sql/block_ref_query.go b/kernel/sql/block_ref_query.go
index f786b8288..bef897f0a 100644
--- a/kernel/sql/block_ref_query.go
+++ b/kernel/sql/block_ref_query.go
@@ -362,9 +362,9 @@ func QueryRefIDsByDefID(defID string, containChildren bool) (refIDs []string) {
 	var rows *sql.Rows
 	var err error
 	if containChildren {
-		rows, err = query("SELECT block_id FROM refs WHERE def_block_root_id = ?", defID)
+		rows, err = query("SELECT DISTINCT block_id FROM refs WHERE def_block_root_id = ?", defID)
 	} else {
-		rows, err = query("SELECT block_id FROM refs WHERE def_block_id = ?", defID)
+		rows, err = query("SELECT DISTINCT block_id FROM refs WHERE def_block_id = ?", defID)
 	}
 	if err != nil {
 		logging.LogErrorf("sql query failed: %s", err)