diff --git a/lib/jekyll/tags/post_url.rb b/lib/jekyll/tags/post_url.rb
index 51b3b605..063e22a4 100644
--- a/lib/jekyll/tags/post_url.rb
+++ b/lib/jekyll/tags/post_url.rb
@@ -50,9 +50,11 @@ module Jekyll
           end
         end
 
-        puts "ERROR: post_url: \"#{@orig_post}\" could not be found"
+        raise ArgumentError.new <<-eos
+Could not find post "#{@orig_post}" in tag 'post_url'.
 
-        return "#"
+Make sure the post exists and the name is correct.
+eos
       end
     end
   end