diff --git a/index.html b/index.html
index 2e25a65..5ae53bf 100644
--- a/index.html
+++ b/index.html
@@ -382,7 +382,10 @@ function linkify( selector ) {
 					{ src: 'lib/js/classList.js', condition: function() { return !document.body.classList; } },
 					{ src: 'plugin/markdown/marked.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
 					{ src: 'plugin/markdown/markdown.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
-					{ src: 'plugin/highlight/highlight.js', async: true, callback: function() { hljs.initHighlightingOnLoad(); } },
+					{ src: 'plugin/highlight/highlight.js', async: true, callback: function() { 
+							hljs.configure({languages:['js','html']}); // limit language detection to what's in the presentation
+							hljs.initHighlightingOnLoad(); 
+					} },
 					{ src: 'plugin/zoom-js/zoom.js', async: true, condition: function() { return !!document.body.classList; } },
 					{ src: 'plugin/notes/notes.js', async: true, condition: function() { return !!document.body.classList; } }
 				]