diff --git a/actionpack/test/controller/fragment_store_setting_test.rb b/actionpack/test/controller/fragment_store_setting_test.rb
index fde70965f6..7d0c0b61aa 100644
--- a/actionpack/test/controller/fragment_store_setting_test.rb
+++ b/actionpack/test/controller/fragment_store_setting_test.rb
@@ -1,6 +1,6 @@
 require File.dirname(__FILE__) + '/../abstract_unit'
 
-MemCache = Struct.new(:MemCache, :address)
+MemCache = Struct.new(:MemCache, :address) unless Object.const_defined?(:MemCache)
 
 class FragmentCacheStoreSettingTest < Test::Unit::TestCase
   def teardown
@@ -42,4 +42,4 @@ def test_object_assigned_fragment_cache_store
     )
     assert_equal "/path/to/cache/directory", ActionController::Base.fragment_cache_store.cache_path
   end
-end
\ No newline at end of file
+end