diff --git a/ChangeLog b/ChangeLog
index 1a00d98796..fd7f1b3625 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Oct 22 16:27:57 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* vm_insnhelper.c (vm_yield_setup_args): should not drop arguments
+	  corresponding to default paramters.
+
 Wed Oct 22 14:59:30 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* parse.y (f_larglist): should not allow semicolon separated local
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 553883c035..2e862492f3 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -728,12 +728,13 @@ vm_yield_setup_args(rb_thread_t * const th, const rb_iseq_t *iseq,
 	}
 
 	if (iseq->arg_rest == -1) {
-	    if (m < argc) {
+	    const int arg_size = iseq->arg_size;
+	    if (arg_size < argc) {
 		/*
 		 * yield 1, 2
 		 * => {|a|} # truncate
 		 */
-		th->mark_stack_len = argc = m;
+		th->mark_stack_len = argc = arg_size;
 	    }
 	}
 	else {