diff --git a/lib/jekyll/tags/highlight.rb b/lib/jekyll/tags/highlight.rb
index d0d70882..027865cd 100644
--- a/lib/jekyll/tags/highlight.rb
+++ b/lib/jekyll/tags/highlight.rb
@@ -111,7 +111,7 @@ eos
       def add_code_tag(code)
         code_attributes = [
           "class=\"language-#{@lang.to_s.tr('+', '-')}\"",
-          "data-lang=\"#{@lang.to_s}\""
+          "data-lang=\"#{@lang}\""
         ].join(" ")
         "<figure class=\"highlight\"><pre><code #{code_attributes}>#{code.chomp}</code></pre></figure>"
       end