diff --git a/lib/plugins/helper/toc.js b/lib/plugins/helper/toc.js
index 01aa7c9fbf..52b5f28481 100644
--- a/lib/plugins/helper/toc.js
+++ b/lib/plugins/helper/toc.js
@@ -32,7 +32,9 @@ function tocHelper(str, options = {}) {
     return id || (parent.length < 1 ? null : getId(parent));
   }
 
-  for (const el of headings) {
+  const headingLen = headings.length;
+  for (let i = 0; i < headingLen; i++) {
+    const el = headings[i];
     const level = +el.name[1];
     const id = getId(el);
     const text = escapeHTML(DomUtils.getText(el));