diff --git a/lib/jekyll/document.rb b/lib/jekyll/document.rb
index b6493f3c..d42e544c 100644
--- a/lib/jekyll/document.rb
+++ b/lib/jekyll/document.rb
@@ -204,7 +204,7 @@ module Jekyll
     #
     # Returns the computed URL for the document.
     def url
-      @url = URL.new({
+      @url ||= URL.new({
         :template     => url_template,
         :placeholders => url_placeholders,
         :permalink    => permalink,