diff --git a/lib/github/markup/markdown.rb b/lib/github/markup/markdown.rb
index f4ef99dc..8ad9722f 100644
--- a/lib/github/markup/markdown.rb
+++ b/lib/github/markup/markdown.rb
@@ -25,7 +25,7 @@ class Markdown < Implementation
       }
 
       def initialize
-        super(/md|mkdn?|mdwn|mdown|markdown|litcoffee/)
+        super(/md|rmd|mkdn?|mdwn|mdown|markdown|litcoffee/i)
       end
 
       def load
diff --git a/test/markup_test.rb b/test/markup_test.rb
index 3269e0d6..392424f7 100644
--- a/test/markup_test.rb
+++ b/test/markup_test.rb
@@ -37,6 +37,8 @@ class MarkupTest < Test::Unit::TestCase
   def test_knows_what_it_can_and_cannot_render
     assert_equal false, GitHub::Markup.can_render?('README.html')
     assert_equal true, GitHub::Markup.can_render?('README.markdown')
+    assert_equal true, GitHub::Markup.can_render?('README.rmd')
+    assert_equal true, GitHub::Markup.can_render?('README.Rmd')
     assert_equal false, GitHub::Markup.can_render?('README.cmd')
     assert_equal true, GitHub::Markup.can_render?('README.litcoffee')
   end
diff --git a/test/markups/README.rmd b/test/markups/README.rmd
new file mode 100644
index 00000000..f9f5f702
--- /dev/null
+++ b/test/markups/README.rmd
@@ -0,0 +1,3 @@
+# Title
+* One
+* Two
diff --git a/test/markups/README.rmd.html b/test/markups/README.rmd.html
new file mode 100644
index 00000000..e712d1c7
--- /dev/null
+++ b/test/markups/README.rmd.html
@@ -0,0 +1,6 @@
+<h1>Title</h1>
+
+<ul>
+<li>One</li>
+<li>Two</li>
+</ul>