diff --git a/kernel/model/box.go b/kernel/model/box.go
index f6ef21498..1020549a3 100644
--- a/kernel/model/box.go
+++ b/kernel/model/box.go
@@ -464,6 +464,10 @@ func parseKTree(kramdown []byte) (ret *parse.Tree) {
 }
 
 func genTreeID(tree *parse.Tree) {
+	if nil == tree.Root.FirstChild {
+		tree.Root.AppendChild(parse.NewParagraph())
+	}
+
 	ast.Walk(tree.Root, func(n *ast.Node, entering bool) ast.WalkStatus {
 		if !entering {
 			return ast.WalkContinue