diff --git a/config.ru b/config.ru
index 6b0326b323e..c74954f4f4b 100644
--- a/config.ru
+++ b/config.ru
@@ -1,3 +1,6 @@
 # This file is used by Rack-based servers to start the application.
 require ::File.expand_path('../config/environment',  __FILE__)
-run Discourse::Application
+map ActionController::Base.config.try(:relative_url_root) || "/" do
+  run Discourse::Application
+end
+