diff --git a/lib/open_id_authentication.rb b/lib/open_id_authentication.rb
index 6b8ff7c..2cebcf6 100644
--- a/lib/open_id_authentication.rb
+++ b/lib/open_id_authentication.rb
@@ -222,7 +222,7 @@ def requested_url
       relative_url_root = self.class.respond_to?(:relative_url_root) ?
         self.class.relative_url_root.to_s :
         request.relative_url_root
-      "#{request.protocol + request.host_with_port + relative_url_root + request.path}"
+      "#{request.protocol}#{request.host_with_port}#{ActionController::Base.relative_url_root}#{request.path}"
     end
 
     def timeout_protection_from_identity_server