diff --git a/lib/jekyll/post.rb b/lib/jekyll/post.rb
index 571d854d..9d10a5cb 100644
--- a/lib/jekyll/post.rb
+++ b/lib/jekyll/post.rb
@@ -76,7 +76,7 @@ module Jekyll
 
     def populate_categories
       if self.categories.empty?
-        self.categories = self.data.pluralized_array('category', 'categories').map {|c| c.downcase}
+        self.categories = self.data.pluralized_array('category', 'categories').map {|c| c.to_s.downcase}
       end
       self.categories.flatten!
     end
diff --git a/test/source/_posts/2013-05-10-number-category.textile b/test/source/_posts/2013-05-10-number-category.textile
new file mode 100644
index 00000000..1a490a88
--- /dev/null
+++ b/test/source/_posts/2013-05-10-number-category.textile
@@ -0,0 +1,7 @@
+---
+layout: default
+title: Number Category in YAML
+category: 2013
+---
+
+Please make me pass
\ No newline at end of file
diff --git a/test/test_generated_site.rb b/test/test_generated_site.rb
index cb8b5486..35c451c5 100644
--- a/test/test_generated_site.rb
+++ b/test/test_generated_site.rb
@@ -14,7 +14,7 @@ class TestGeneratedSite < Test::Unit::TestCase
     end
 
     should "ensure post count is as expected" do
-      assert_equal 33, @site.posts.size
+      assert_equal 34, @site.posts.size
     end
 
     should "insert site.posts into the index" do
diff --git a/test/test_post.rb b/test/test_post.rb
index b28af071..9ea972a8 100644
--- a/test/test_post.rb
+++ b/test/test_post.rb
@@ -422,6 +422,12 @@ class TestPost < Test::Unit::TestCase
         post = setup_post("2009-01-27-empty-categories.textile")
         assert_equal [], post.categories
       end
+      
+      should "recognize number category in yaml" do
+        post = setup_post("2013-05-10-number-category.textile")
+        assert post.categories.include?('2013')
+        assert !post.categories.include?(2013)
+      end
 
       should "recognize tag in yaml" do
         post = setup_post("2009-05-18-tag.textile")
diff --git a/test/test_site.rb b/test/test_site.rb
index 37fec83f..4e46ba7f 100644
--- a/test/test_site.rb
+++ b/test/test_site.rb
@@ -172,7 +172,7 @@ class TestSite < Test::Unit::TestCase
 
       posts = Dir[source_dir("**", "_posts", "**", "*")]
       posts.delete_if { |post| File.directory?(post) && !Post.valid?(post) }
-      categories = %w(bar baz category foo z_category publish_test win).sort
+      categories = %w(2013 bar baz category foo z_category publish_test win).sort
 
       assert_equal posts.size - @num_invalid_posts, @site.posts.size
       assert_equal categories, @site.categories.keys.sort