diff --git a/ChangeLog b/ChangeLog
index a11b947149..c5f6dac7b5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,9 @@
-Fri Jul 29 23:53:44 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Fri Jul 29 23:53:48 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* array.c (rb_ary_set_len): new function to set array length.
+
+	* vm_eval.c (method_missing): set the length of argv array, to mark
+	  arguments.
 
 	* vm_eval.c (rb_apply): get rid of too large alloca.
 
diff --git a/array.c b/array.c
index 09c9883b13..8caad66a3e 100644
--- a/array.c
+++ b/array.c
@@ -1310,6 +1310,21 @@ rb_ary_splice(VALUE ary, long beg, long len, VALUE rpl)
     }
 }
 
+void
+rb_ary_set_len(VALUE ary, long len)
+{
+    long capa;
+
+    rb_ary_modify_check(ary);
+    if (ARY_SHARED_P(ary)) {
+	rb_raise(rb_eRuntimeError, "can't set length of shared ");
+    }
+    if (len > (capa = (long)ARY_CAPA(ary))) {
+	rb_bug("probable buffer overflow: %ld for %ld", len, capa);
+    }
+    ARY_SET_LEN(ary, len);
+}
+
 /*!
  * expands or shrinks \a ary to \a len elements.
  * expanded region will be filled with Qnil.
diff --git a/internal.h b/internal.h
index 59340d2884..dad96606db 100644
--- a/internal.h
+++ b/internal.h
@@ -41,6 +41,7 @@ struct vtm; /* defined by timev.h */
 
 /* array.c */
 VALUE rb_ary_last(int, VALUE *, VALUE);
+void rb_ary_set_len(VALUE, long);
 
 /* bignum.c */
 VALUE rb_big_fdiv(VALUE x, VALUE y);
diff --git a/vm_eval.c b/vm_eval.c
index 8ce268d8f9..b4234e0f63 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -568,6 +568,7 @@ method_missing(VALUE obj, ID id, int argc, const VALUE *argv, int call_status)
     }
     nargv[0] = ID2SYM(id);
     MEMCPY(nargv + 1, argv, VALUE, argc);
+    if (argv_ary) rb_ary_set_len(argv_ary, argc + 1);
 
     if (rb_method_basic_definition_p(CLASS_OF(obj) , idMethodMissing)) {
 	raise_method_missing(th, argc+1, nargv, obj, call_status | NOEX_MISSING);