1 files changed, 11 insertions, 5 deletions
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 846a6345cb..18f37dc732 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -3,6 +3,7 @@ require 'active_support/core_ext/hash/reverse_merge'
 require 'active_support/core_ext/hash/slice'
 require 'active_support/core_ext/enumerable'
 require 'active_support/core_ext/array/extract_options'
+require 'active_support/core_ext/module/remove_method'
 require 'active_support/inflector'
 require 'action_dispatch/routing/redirection'
 
@@ -217,8 +218,12 @@ module ActionDispatch
               controller ||= default_controller
               action     ||= default_action
 
-              unless controller.is_a?(Regexp)
-                controller = [@scope[:module], controller].compact.join("/").presence
+              if @scope[:module] && !controller.is_a?(Regexp)
+                if controller =~ %r{\A/}
+                  controller = controller[1..-1]
+                else
+                  controller = [@scope[:module], controller].compact.join("/").presence
+                end
               end
 
               if controller.is_a?(String) && controller =~ %r{\A/}
@@ -502,11 +507,12 @@ module ActionDispatch
           raise "A rack application must be specified" unless path
 
           options[:as]  ||= app_name(app)
+          target_as       = name_for_action(options[:as], path)
           options[:via] ||= :all
 
           match(path, options.merge(:to => app, :anchor => false, :format => false))
 
-          define_generate_prefix(app, options[:as])
+          define_generate_prefix(app, target_as)
           self
         end
 
@@ -545,11 +551,11 @@ module ActionDispatch
             _routes = @set
             app.routes.define_mounted_helper(name)
             app.routes.singleton_class.class_eval do
-              define_method :mounted? do
+              redefine_method :mounted? do
                 true
               end
 
-              define_method :_generate_prefix do |options|
+              redefine_method :_generate_prefix do |options|
                 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) }