diff --git a/ChangeLog b/ChangeLog
index 6efb99be0e..2e845fb0e8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri May 25 17:05:07 2012  Koichi Sasada  <ko1@atdot.net>
+
+	* vm.c (oldbt_init, vm_backtrace_str_ary): arg->data should
+	  be initialized before calling `backtrace_each()'.
+
 Fri May 25 16:11:27 2012  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* trunk/ext/-test-/printf/printf.c: change function names because of
diff --git a/vm.c b/vm.c
index a6f1ce5a47..54c57969b3 100644
--- a/vm.c
+++ b/vm.c
@@ -1090,7 +1090,6 @@ oldbt_init(void *ptr, int dmy)
 
     arg->filename = th->vm->progname ? th->vm->progname : ruby_engine_name;;
     arg->line_no = 0;
-    arg->data = (void *)rb_ary_new();
 }
 
 static void
@@ -1142,6 +1141,7 @@ vm_backtrace_str_ary(rb_thread_t *th, size_t lev, size_t n)
     VALUE *ptr;
 
     arg.func = oldbt_push;
+    arg.data = (void *)rb_ary_new();
 
     backtrace_each(th,
 		   oldbt_init,