diff --git a/lib/jekyll/tags/post_url.rb b/lib/jekyll/tags/post_url.rb
index 0f92df49..ce97642f 100644
--- a/lib/jekyll/tags/post_url.rb
+++ b/lib/jekyll/tags/post_url.rb
@@ -3,16 +3,22 @@ module Jekyll
     class PostComparer
       MATCHER = /^(.+\/)*(\d+-\d+-\d+)-(.*)$/
 
-      attr_accessor :date, :slug
+      attr_reader :path, :date, :slug, :name
 
       def initialize(name)
-        all, path, date, slug = *name.sub(/^\//, "").match(MATCHER)
+        @name = name
+        all, @path, @date, @slug = *name.sub(/^\//, "").match(MATCHER)
         raise ArgumentError.new("'#{name}' does not contain valid date and/or title.") unless all
-        @slug = path ? path + slug : slug
-        @date = Utils.parse_date(date, "'#{name}' does not contain valid date.")
+
+        @name_regex = /^#{path}#{date}-#{slug}\.[^.]+/
       end
 
       def ==(other)
+        other.name.match(@name_regex)
+      end
+
+      def deprecated_equality(other)
+        date = Utils.parse_date(name, "'#{name}' does not contain valid date and/or title.")
         slug == post_slug(other) &&
           date.year  == other.date.year &&
           date.month == other.date.month &&
@@ -59,6 +65,19 @@ eos
           end
         end
 
+        # New matching method did not match, fall back to old method
+        # with deprecation warning if this matches
+
+        site.posts.each do |p|
+          if @post.deprecated_equality p
+            Jekyll::Deprecator.deprecation_message "A call to '{{ post_url #{name} }}' did not match " +
+              "a post using the new matching method of checking name " +
+              "(path-date-slug) equality. Please make sure that you " +
+              "change this tag to match the post's name exactly."
+            return p.url
+          end
+        end
+
         raise ArgumentError.new <<-eos
 Could not find post "#{@orig_post}" in tag 'post_url'.