diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 21dc5af486..4d65173f61 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -452,7 +452,9 @@ module ActionDispatch
                 prefix_options = options.slice(*_route.segment_keys)
                 # we must actually delete prefix segment keys to avoid passing them to next url_for
                 _route.segment_keys.each { |k| options.delete(k) }
-                _routes.url_helpers.send("#{name}_path", prefix_options)
+                prefix = _routes.url_helpers.send("#{name}_path", prefix_options)
+                prefix = '' if prefix == '/'
+                prefix
               end
             end
           end
diff --git a/railties/test/railties/mounted_engine_test.rb b/railties/test/railties/mounted_engine_test.rb
index 94dec405a7..253e61259b 100644
--- a/railties/test/railties/mounted_engine_test.rb
+++ b/railties/test/railties/mounted_engine_test.rb
@@ -11,13 +11,17 @@ module ApplicationTests
 
       add_to_config("config.action_dispatch.show_exceptions = false")
 
+      @simple_plugin = engine "weblog"
       @plugin = engine "blog"
 
       app_file 'config/routes.rb', <<-RUBY
         AppTemplate::Application.routes.draw do
+          mount Weblog::Engine, :at => '/', :as => 'weblog'
           resources :posts
           match "/engine_route" => "application_generating#engine_route"
           match "/engine_route_in_view" => "application_generating#engine_route_in_view"
+          match "/weblog_engine_route" => "application_generating#weblog_engine_route"
+          match "/weblog_engine_route_in_view" => "application_generating#weblog_engine_route_in_view"
           match "/url_for_engine_route" => "application_generating#url_for_engine_route"
           match "/polymorphic_route" => "application_generating#polymorphic_route"
           match "/application_polymorphic_path" => "application_generating#application_polymorphic_path"
@@ -28,6 +32,29 @@ module ApplicationTests
         end
       RUBY
 
+
+      @simple_plugin.write "lib/weblog.rb", <<-RUBY
+        module Weblog
+          class Engine < ::Rails::Engine
+          end
+        end
+      RUBY
+
+      @simple_plugin.write "config/routes.rb", <<-RUBY
+        Weblog::Engine.routes.draw do
+          match '/weblog' => "weblogs#index", :as => 'weblogs'
+        end
+      RUBY
+
+      @simple_plugin.write "app/controllers/weblogs_controller.rb", <<-RUBY
+        class WeblogsController < ActionController::Base
+          def index
+            render :text => request.url
+          end
+        end
+      RUBY
+
+
       @plugin.write "app/models/blog/post.rb", <<-RUBY
         module Blog
           class Post
@@ -100,6 +127,14 @@ module ApplicationTests
             render :inline => "<%= blog.posts_path %>"
           end
 
+          def weblog_engine_route
+            render :text => weblog.weblogs_path
+          end
+
+          def weblog_engine_route_in_view
+            render :inline => "<%= weblog.weblogs_path %>"
+          end
+
           def url_for_engine_route
             render :text => blog.url_for(:controller => "blog/posts", :action => "index", :user => "john", :only_path => true)
           end
@@ -192,5 +227,18 @@ module ApplicationTests
       get "/application_polymorphic_path"
       assert_equal "/posts/44", last_response.body
     end
+
+    test "route path for controller action when engine is mounted at root" do
+      get "/weblog_engine_route"
+      assert_equal "/weblog", last_response.body
+
+      get "/weblog_engine_route_in_view"
+      assert_equal "/weblog", last_response.body
+    end
+
+    test "request url for controller action when engine is mounted at root" do
+      get "/weblog"
+      assert_equal "http://example.org/weblog", last_response.body
+    end
   end
 end