diff --git a/test/ruby/test_rubyvm.rb b/test/ruby/test_rubyvm.rb
index 613cfe2161..580f3be2e1 100644
--- a/test/ruby/test_rubyvm.rb
+++ b/test/ruby/test_rubyvm.rb
@@ -12,5 +12,6 @@ class TestRubyVM < Test::Unit::TestCase
 
   def test_stat_unknown
     assert_raise(ArgumentError){ RubyVM.stat(:unknown) }
+    assert_raise_with_message(ArgumentError, /\u{30eb 30d3 30fc}/) {RubyVM.stat(:"\u{30eb 30d3 30fc}")}
   end
 end
diff --git a/vm.c b/vm.c
index 5b4aa6fae0..1742cc5008 100644
--- a/vm.c
+++ b/vm.c
@@ -173,8 +173,9 @@ vm_stat(int argc, VALUE *argv, VALUE self)
     SET(class_serial, ruby_vm_class_serial);
 #undef SET
 
-    if (key != Qnil) /* matched key should return above */
-	rb_raise(rb_eArgError, "unknown key: %s", RSTRING_PTR(rb_id2str(SYM2ID(key))));
+    if (!NIL_P(key)) { /* matched key should return above */
+	rb_raise(rb_eArgError, "unknown key: %"PRIsVALUE, rb_sym2str(key));
+    }
 
     return hash;
 }