diff --git a/addons/web_editor/static/src/js/widgets/ace.js b/addons/web_editor/static/src/js/widgets/ace.js
index 6c28c1e2332..0a89d0d8ce7 100644
--- a/addons/web_editor/static/src/js/widgets/ace.js
+++ b/addons/web_editor/static/src/js/widgets/ace.js
@@ -742,7 +742,7 @@ var ViewEditor = Widget.extend({
 
             var text = data.text || '';
             if (!isSelected) {
-                text = Array($elem.data('level') + 1).join('-') + ' ' + text;
+                text = Array(($elem.data('level') || 0) + 1).join('-') + ' ' + text;
             }
             var $div = $('<div/>',  {
                 text: text,