diff --git a/lib/jekyll/converters/markdown/redcarpet_parser.rb b/lib/jekyll/converters/markdown/redcarpet_parser.rb
index 7a805fe9..cf6c88ca 100644
--- a/lib/jekyll/converters/markdown/redcarpet_parser.rb
+++ b/lib/jekyll/converters/markdown/redcarpet_parser.rb
@@ -5,6 +5,7 @@ module Jekyll
 
         module CommonMethods
           def add_code_tags(code, lang)
+            code = code.to_s
             code = code.sub(/<pre>/, "<pre><code class=\"#{lang} language-#{lang}\" data-lang=\"#{lang}\">")
             code = code.sub(/<\/pre>/,"</code></pre>")
           end