diff --git a/lib/jekyll/tags/highlight.rb b/lib/jekyll/tags/highlight.rb
index e8059edb..2ea144df 100644
--- a/lib/jekyll/tags/highlight.rb
+++ b/lib/jekyll/tags/highlight.rb
@@ -14,7 +14,7 @@ module Jekyll
       def initialize(tag_name, markup, tokens)
         super
         if markup.strip =~ SYNTAX
-          @lang = $1
+          @lang = $1.downcase
           @options = {}
           if defined?($2) && $2 != ''
             $2.split.each do |opt|
diff --git a/test/test_tags.rb b/test/test_tags.rb
index fe16faa5..135bdd10 100644
--- a/test/test_tags.rb
+++ b/test/test_tags.rb
@@ -69,6 +69,9 @@ CONTENT
 
       tag = Jekyll::Tags::HighlightBlock.new('highlight', 'ruby linenos=table cssclass=hl', ["test", "{% endhighlight %}", "\n"])
       assert_equal({ 'cssclass' => 'hl', 'linenos' => 'table' }, tag.instance_variable_get(:@options))
+
+      tag = Jekyll::Tags::HighlightBlock.new('highlight', 'Ruby ', ["test", "{% endhighlight %}", "\n"])
+      assert_equal "ruby", tag.instance_variable_get(:@lang), "lexers should be case insensitive"
     end
   end