diff --git a/test/-ext-/test_notimplement.rb b/test/-ext-/test_notimplement.rb
index 80757313ca..ca09234211 100644
--- a/test/-ext-/test_notimplement.rb
+++ b/test/-ext-/test_notimplement.rb
@@ -12,4 +12,8 @@ class Test_NotImplement < Test::Unit::TestCase
   def test_respond_to
     assert_not_respond_to(Bug, :notimplement)
   end
+
+  def test_not_method_defined
+    assert !Bug.method_defined?(:notimplement)
+  end
 end