diff --git a/activesupport/test/core_ext/duplicable_test.rb b/activesupport/test/core_ext/duplicable_test.rb
index 0ed81fa8e1762..3e54266051f8a 100644
--- a/activesupport/test/core_ext/duplicable_test.rb
+++ b/activesupport/test/core_ext/duplicable_test.rb
@@ -22,7 +22,7 @@ def test_duplicable
     end
 
     RAISE_DUP.each do |v|
-      assert_raises(TypeError) do
+      assert_raises(TypeError, v.class.name) do
         v.dup
       end
     end