diff --git a/lib/jekyll/converters/markdown/redcarpet_parser.rb b/lib/jekyll/converters/markdown/redcarpet_parser.rb
index 03d659c4..ce4a303d 100644
--- a/lib/jekyll/converters/markdown/redcarpet_parser.rb
+++ b/lib/jekyll/converters/markdown/redcarpet_parser.rb
@@ -19,7 +19,7 @@ module Jekyll
             end
 
             def add_code_tags(code, lang)
-              code = code.sub(/<pre>/,'<pre><code class="' + lang + '">')
+              code = code.sub(/<pre>/,'<pre><code class="language-' + lang + '">')
               code = code.sub(/<\/pre>/,"</code></pre>")
             end
           end