2 files changed, 14 insertions, 1 deletions
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index fd37fd0457..83cee28fa3 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -528,7 +528,7 @@ module Rails
     # Defines the routes for this engine. If a block is given to
     # routes, it is appended to the engine.
     def routes
-      @routes ||= ActionDispatch::Routing::RouteSet.new
+      @routes ||= ActionDispatch::Routing::RouteSet.new_with_config(config)
       @routes.append(&Proc.new) if block_given?
       @routes
     end
diff --git a/railties/test/application/url_generation_test.rb b/railties/test/application/url_generation_test.rb
index ef16ab56ed..894e18cb39 100644
--- a/railties/test/application/url_generation_test.rb
+++ b/railties/test/application/url_generation_test.rb
@@ -42,5 +42,18 @@ module ApplicationTests
       get "/"
       assert_equal "/", last_response.body
     end
+
+    def test_routes_know_the_relative_root
+      boot_rails
+      require "rails"
+      require "action_controller/railtie"
+      require "action_view/railtie"
+
+      relative_url = '/hello'
+      ENV["RAILS_RELATIVE_URL_ROOT"] = relative_url
+      app = Class.new(Rails::Application)
+      assert_equal relative_url, app.routes.relative_url_root
+      ENV["RAILS_RELATIVE_URL_ROOT"] = nil
+    end
   end
 end