2 files changed, 9 insertions, 2 deletions
diff --git a/marshal.c b/marshal.c
index 1fae54530a..b38c53c05c 100644
--- a/marshal.c
+++ b/marshal.c
@@ -904,8 +904,8 @@ w_object(VALUE obj, struct dump_arg *arg, int limit)
 	    break;
 
 	  default:
-	    rb_raise(rb_eTypeError, "can't dump %s",
-		     rb_obj_classname(obj));
+	    rb_raise(rb_eTypeError, "can't dump %"PRIsVALUE,
+		     rb_obj_class(obj));
 	    break;
 	}
 	RB_GC_GUARD(obj);
diff --git a/test/ruby/test_marshal.rb b/test/ruby/test_marshal.rb
index 3d5d6c9b1f..c8d79edb02 100644
--- a/test/ruby/test_marshal.rb
+++ b/test/ruby/test_marshal.rb
@@ -647,4 +647,11 @@ class TestMarshal < Test::Unit::TestCase
       c.cc.call
     end
   end
+
+  def test_undumpable_message
+    c = Module.new {break module_eval("class IO\u{26a1} < IO;self;end")}
+    assert_raise_with_message(TypeError, /IO\u{26a1}/) {
+      Marshal.dump(c.new(0, autoclose: false))
+    }
+  end
 end