diff --git a/ChangeLog b/ChangeLog
index 6033fe9e48..1c35787ac9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Aug 28 20:22:49 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* vm_insnhelper.c (vm_yield_setup_args): object with to_ary should
+	  behave like array.  a patch from Yusuke Endoh  <mame at tsg.ne.jp>
+	  in [ruby-dev:35988].  [ruby-dev:35977]
+
 Thu Aug 28 19:04:50 2008  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* bootstraptest/test_io.rb: no need to create real file.
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 07fe32d2a2..f40d6a2414 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -704,6 +704,7 @@ vm_yield_setup_args(rb_thread_t * const th, const rb_iseq_t *iseq,
 	int i;
 	int argc = orig_argc;
 	const int m = iseq->argc;
+	VALUE ary;
 
 	th->mark_stack_len = argc;
 
@@ -714,8 +715,7 @@ vm_yield_setup_args(rb_thread_t * const th, const rb_iseq_t *iseq,
 	 */
 	if (!(iseq->arg_simple & 0x02) &&
 	    (m + iseq->arg_post_len) > 0 &&
-	    argc == 1 && TYPE(argv[0]) == T_ARRAY) {
-	    VALUE ary = argv[0];
+	    argc == 1 && !NIL_P(ary = rb_check_array_type(argv[0]))) {
 	    th->mark_stack_len = argc = RARRAY_LEN(ary);
 
 	    CHECK_STACK_OVERFLOW(th->cfp, argc);