diff --git a/lib/markdown-pdf.js b/lib/markdown-pdf.js
index 244e7d9..0ff40e8 100644
--- a/lib/markdown-pdf.js
+++ b/lib/markdown-pdf.js
@@ -30,6 +30,8 @@ function markdownpdf (opts) {
   var markedOptions = {
     highlight: function (code, lang) {
 
+      lang = lang.toLowerCase();
+
       if (lang && !highlight.getLanguage(lang)) {
         return code;
       }