diff --git a/activesupport/test/file_update_checker_with_enumerable_test_cases.rb b/activesupport/test/file_update_checker_with_enumerable_test_cases.rb
index <HASH>..<HASH> 100644
--- a/activesupport/test/file_update_checker_with_enumerable_test_cases.rb
+++ b/activesupport/test/file_update_checker_with_enumerable_test_cases.rb
@@ -13,7 +13,7 @@ module FileUpdateCheckerWithEnumerableTestCases
   end
 
   def setup
-    @tmpdir = Dir.mktmpdir
+    @tmpdir = Dir.mktmpdir(nil, __dir__)
 
     @files = %w(foo.rb bar.rb baz.rb).map {|f| "#{@tmpdir}/#{f}"}
     FileUtils.touch(@files)
create the tmpdir under test

Mac OS X tries by all means to hide that /var is /private/var, and that is
what FSEvents reports back.