diff --git a/docs/02_lesson.html b/docs/02_lesson.html
index 8018ce6..5edd03c 100644
--- a/docs/02_lesson.html
+++ b/docs/02_lesson.html
@@ -98,7 +98,7 @@
   }
 }</script>
 
-  <script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script>
+  <script src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js?version=3&features=es6"></script>
   <script src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml-full.js" type="text/javascript"></script>
 
 <link rel="stylesheet" href="style.scss">