diff --git a/test/ruby/test_refinement.rb b/test/ruby/test_refinement.rb
index 11acf31f21..913c968d35 100644
--- a/test/ruby/test_refinement.rb
+++ b/test/ruby/test_refinement.rb
@@ -825,7 +825,7 @@ class TestRefinement < Test::Unit::TestCase
       GC.stress = true
       10.times{
         #{PrependAfterRefine_CODE}
-        undef PrependAfterRefine
+        Object.send(:remove_const, :PrependAfterRefine)
       }
     }, timeout: 60
   end