diff --git a/lib/jekyll/post.rb b/lib/jekyll/post.rb
index 835f9a42..b08021d0 100644
--- a/lib/jekyll/post.rb
+++ b/lib/jekyll/post.rb
@@ -154,7 +154,7 @@ module Jekyll
           "title"      => CGI.escape(slug),
           "i_day"      => date.strftime("%d").to_i.to_s,
           "i_month"    => date.strftime("%m").to_i.to_s,
-          "categories" => categories.map { |c| URI.escape(c) }.join('/'),
+          "categories" => categories.map { |c| URI.escape(c.to_s) }.join('/'),
           "output_ext" => self.output_ext
         }.inject(template) { |result, token|
           result.gsub(/:#{Regexp.escape token.first}/, token.last)
diff --git a/test/test_post.rb b/test/test_post.rb
index 16aff4f1..582fc80c 100644
--- a/test/test_post.rb
+++ b/test/test_post.rb
@@ -128,6 +128,18 @@ class TestPost < Test::Unit::TestCase
           end
         end
 
+        context "with unspecified (date) style and a numeric category" do
+          setup do
+            @post.categories << 2013
+            @post.process(@fake_file)
+          end
+
+          should "process the url correctly" do
+            assert_equal "/:categories/:year/:month/:day/:title.html", @post.template
+            assert_equal "/2013/2008/09/09/foo-bar.html", @post.url
+          end
+        end
+
         context "with unspecified layout" do
           setup do
             file = '2013-01-12-no-layout.textile'