diff --git a/ChangeLog b/ChangeLog
index 28490d60aa..5f71e98991 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jul 29 15:44:47 2012  CHIKANAGA Tomoyuki  <nagachika@ruby-lang.org>
+
+	* thread.c (thread_create_core): hide th->async_errinfo_mask_stack from
+	  ObjectSpace.each_object. refix of r36539.
+
 Sun Jul 29 23:57:27 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/socket/option.c (inet_ntop): use rb_w32_inet_ntop, instead of
diff --git a/thread.c b/thread.c
index e4506c2374..d68fead92e 100644
--- a/thread.c
+++ b/thread.c
@@ -565,6 +565,7 @@ thread_create_core(VALUE thval, VALUE args, VALUE (*fn)(ANYARGS))
     th->async_errinfo_queue = rb_ary_tmp_new(0);
     th->async_errinfo_queue_checked = 0;
     th->async_errinfo_mask_stack = rb_ary_dup(current_th->async_errinfo_mask_stack);
+    RBASIC(th->async_errinfo_mask_stack)->klass = 0;
 
     native_mutex_initialize(&th->interrupt_lock);
     if (GET_VM()->event_hooks != NULL)