diff --git a/Library/Homebrew/test/testing_env.rb b/Library/Homebrew/test/testing_env.rb
index 4e071c000f..57f8971fa7 100644
--- a/Library/Homebrew/test/testing_env.rb
+++ b/Library/Homebrew/test/testing_env.rb
@@ -107,7 +107,7 @@ module Test::Unit::Assertions
   def assert_empty(obj, msg=nil)
     assert_respond_to(obj, :empty?, msg)
     assert(obj.empty?, msg)
-  end if RUBY_VERSION.to_f <= 1.8
+  end unless method_defined?(:assert_empty)
 end
 
 class Test::Unit::TestCase