diff --git a/lib/rack/flash.rb b/lib/rack/flash.rb
index b9b99fd..ea973cb 100644
--- a/lib/rack/flash.rb
+++ b/lib/rack/flash.rb
@@ -1,27 +1,34 @@
 module Rack
   class Builder
-    attr :ins
     def use(middleware, *args, &block)
+      # Begin monkey patch
       middleware.instance_variable_set "@rack_builder", self
       def middleware.rack_builder
         @rack_builder
       end
-      @ins << lambda { |app|
-        middleware.new(app, *args, &block)
-      }
+      # End monkey patch
+
+      if @map
+        mapping, @map = @map, nil
+        @use << proc { |app| generate_map app, mapping }
+      end
+      @use << proc { |app| middleware.new(app, *args, &block) }
     end
 
     def run(app)
+      # Begin monkey patch
       klass = app.class
       klass.instance_variable_set "@rack_builder", self
       def klass.rack_builder
         @rack_builder
       end
-      @ins << app #lambda { |nothing| app }
+      # End monkey patch
+
+      @run = app
     end
 
     def leaf_app
-      ins.last
+      @run
     end
   end
 end