diff --git a/website/themes/nnja-theme-learn/static/js/learn.js b/website/themes/nnja-theme-learn/static/js/learn.js
index 48b1029..1b4da81 100644
--- a/website/themes/nnja-theme-learn/static/js/learn.js
+++ b/website/themes/nnja-theme-learn/static/js/learn.js
@@ -8,7 +8,10 @@ $("pre code").each(function (i, e) {
     var code = $(e);
     var pre = code.parent();
 
-    var language = code.attr('class').replace('language-', '');
+    var className = code.attr('class');
+    if(!className) return;
+
+    var language = className.replace('language-', '');
     var text_block = pre.text();
 
     is_python_repl = text_block.includes(">>> ");