diff --git a/marshal.c b/marshal.c
index b38c53c05c..958778377d 100644
--- a/marshal.c
+++ b/marshal.c
@@ -893,8 +893,8 @@ w_object(VALUE obj, struct dump_arg *arg, int limit)
 
 		if (!rb_obj_respond_to(obj, s_dump_data, TRUE)) {
 		    rb_raise(rb_eTypeError,
-			     "no _dump_data is defined for class %s",
-			     rb_obj_classname(obj));
+			     "no _dump_data is defined for class %"PRIsVALUE,
+			     rb_obj_class(obj));
 		}
 		v = rb_funcall2(obj, s_dump_data, 0, 0);
 		check_dump_arg(arg, s_dump_data);
diff --git a/test/ruby/test_marshal.rb b/test/ruby/test_marshal.rb
index c8d79edb02..115c6bcc5b 100644
--- a/test/ruby/test_marshal.rb
+++ b/test/ruby/test_marshal.rb
@@ -654,4 +654,11 @@ class TestMarshal < Test::Unit::TestCase
       Marshal.dump(c.new(0, autoclose: false))
     }
   end
+
+  def test_undumpable_data
+    c = Module.new {break module_eval("class T\u{23F0 23F3}<Time;undef _dump;self;end")}
+    assert_raise_with_message(TypeError, /T\u{23F0 23F3}/) {
+      Marshal.dump(c.new)
+    }
+  end
 end