diff --git a/actionpack/lib/action_controller/routing/route_set.rb b/actionpack/lib/action_controller/routing/route_set.rb
index 5bc13cf..cc7c699 100644
--- a/actionpack/lib/action_controller/routing/route_set.rb
+++ b/actionpack/lib/action_controller/routing/route_set.rb
@@ -202,8 +202,8 @@ module ActionController
         @builder ||= RouteBuilder.new
       end
 
-      def draw
-        clear!
+      def draw(clear = true)
+        clear! if clear
         yield Mapper.new(self)
         install_helpers
       end
diff --git a/actionpack/test/controller/routing_test.rb b/actionpack/test/controller/routing_test.rb
index 07c13eb..b5dda5f 100644
--- a/actionpack/test/controller/routing_test.rb
+++ b/actionpack/test/controller/routing_test.rb
@@ -1610,6 +1610,27 @@ uses_mocha 'LegacyRouteSet, Route, RouteSet and RouteLoading' do
       assert_equal 1, set.routes.size
     end
 
+    def test_draw_default_clear_parameter
+      set.expects(:clear!).once
+      set.draw do |map|
+        map.connect '/hello/world', :controller => 'a', :action => 'b'
+      end
+    end
+    
+    def test_draw_clear_parameter_is_false
+      set.expects(:clear!).never
+      set.draw(false) do |map|
+        map.connect '/hello/world', :controller => 'a', :action => 'b'
+      end
+    end
+    
+    def test_draw_clear_parameter_is_true
+      set.expects(:clear!).once
+      set.draw(true) do |map|
+        map.connect '/hello/world', :controller => 'a', :action => 'b'
+      end
+    end
+
     def test_named_draw
       assert_equal 0, set.routes.size
       set.draw do |map|