diff --git a/lib/jekyll/post.rb b/lib/jekyll/post.rb
index 7bee2b6c..e5709300 100644
--- a/lib/jekyll/post.rb
+++ b/lib/jekyll/post.rb
@@ -160,7 +160,7 @@ module Jekyll
     def process(name)
       m, cats, date, slug, ext = *name.match(MATCHER)
       self.categories ||= []
-      self.categories += (cats || '').split('/')
+      self.categories += (cats || '').downcase.split('/')
       self.date = Time.parse(date)
       self.slug = slug
       self.ext = ext
diff --git a/test/test_post.rb b/test/test_post.rb
index ac3066b7..bf9b741c 100644
--- a/test/test_post.rb
+++ b/test/test_post.rb
@@ -85,7 +85,7 @@ class TestPost < Test::Unit::TestCase
 
         post = Post.allocate
         post.site = @site
-        post.process("cat2/cat3/2008-09-09-foo-bar.textile")
+        post.process("cat2/CAT3/2008-09-09-foo-bar.textile")
         assert_equal 2, post.categories.size
         assert_equal "cat2", post.categories[0]
         assert_equal "cat3", post.categories[1]