diff --git a/ChangeLog b/ChangeLog
index 4d8f1bc4e2..98ddd10553 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Feb  3 23:13:34 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* vm.c (vm_backtrace): always returns non-nil array if lev is
+	  negative.  [ruby-core:21795]
+
 Tue Feb  3 21:19:06 2009  TAKAO Kouji  <kouji@takao7.net>
 
 	* ext/readline/extconf.rb: checked rl_set_screen_size and
diff --git a/vm.c b/vm.c
index e73ba39d6a..a49926bef1 100644
--- a/vm.c
+++ b/vm.c
@@ -737,6 +737,9 @@ vm_backtrace(rb_thread_t *th, int lev)
 {
     VALUE ary = 0;
 
+    if (lev < 0) {
+	ary = rb_ary_new();
+    }
     vm_backtrace_each(th, lev, vm_backtrace_push, &ary);
     if (!ary) return Qnil;
     return rb_ary_reverse(ary);