diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index b3700ed26479e85b555dc1836e028f18c40a8262..b5c30432cdba987381973a146b8a27ac29592ffd 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -355,7 +355,7 @@ def split_to(to)
 
           def add_controller_module(controller, modyoule)
             if modyoule && !controller.is_a?(Regexp)
-              if %r{\A/}.match?(controller)
+              if controller.to_s.start_with?("/")
                 controller[1..-1]
               else
                 [modyoule, controller].compact.join("/")