diff --git a/railties/lib/rails/configuration.rb b/railties/lib/rails/configuration.rb
index 8369795e71..66fab0a760 100644
--- a/railties/lib/rails/configuration.rb
+++ b/railties/lib/rails/configuration.rb
@@ -1,5 +1,6 @@
 require 'active_support/deprecation'
 require 'active_support/ordered_options'
+require 'active_support/core_ext/hash/deep_dup'
 require 'rails/paths'
 require 'rails/rack'
 
@@ -51,6 +52,13 @@ module Rails
         @colorize_logging = true
       end
 
+      def initialize_copy(source)
+        @aliases = @aliases.deep_dup
+        @options = @options.deep_dup
+        @fallbacks = @fallbacks.deep_dup
+        @templates = @templates.dup
+      end
+
       def method_missing(method, *args)
         method = method.to_s.sub(/=$/, '').to_sym
 
diff --git a/railties/lib/rails/engine/configuration.rb b/railties/lib/rails/engine/configuration.rb
index 5607628d96..4f458b0aee 100644
--- a/railties/lib/rails/engine/configuration.rb
+++ b/railties/lib/rails/engine/configuration.rb
@@ -10,7 +10,7 @@ module Rails
       def initialize(root=nil)
         super()
         @root = root
-        @generators = app_generators
+        @generators = app_generators.dup
       end
 
       # Returns the middleware stack for the engine.
diff --git a/railties/test/railties/engine_test.rb b/railties/test/railties/engine_test.rb
index 3509f964eb..822be24ef1 100644
--- a/railties/test/railties/engine_test.rb
+++ b/railties/test/railties/engine_test.rb
@@ -701,6 +701,9 @@ module RailtiesTest
       generators = Bukkits::Engine.config.generators.options[:rails]
       assert_equal :active_record, generators[:orm]
       assert_equal :rspec        , generators[:test_framework]
+
+      app_generators = Rails.application.config.generators.options[:rails]
+      assert_equal :test_unit    , app_generators[:test_framework]
     end
   end
 end