diff --git a/ChangeLog b/ChangeLog
index ed6f8f06ef..6d473d4df5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Jul 26 00:42:23 2012  CHIKANAGA Tomoyuki  <nagachika@ruby-lang.org>
+
+	* thread.c (thread_create_core, Init_Thread): hide
+	  th->async_errinfo_queue and th->async_errinfo_mask_stack from
+	  ObjectSpace.each_object.
+
 Wed Jul 25 17:41:05 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* complex.c, rational.c: compatible marshal loader for compatibilities
diff --git a/thread.c b/thread.c
index 1cc13a87dd..13c8942368 100644
--- a/thread.c
+++ b/thread.c
@@ -562,7 +562,7 @@ thread_create_core(VALUE thval, VALUE args, VALUE (*fn)(ANYARGS))
     th->priority = current_th->priority;
     th->thgroup = current_th->thgroup;
 
-    th->async_errinfo_queue = rb_ary_new();
+    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);
 
@@ -5123,9 +5123,10 @@ Init_Thread(void)
 	    gvl_acquire(th->vm, th);
 	    native_mutex_initialize(&th->interrupt_lock);
 
-	    th->async_errinfo_queue = rb_ary_new();
+	    th->async_errinfo_queue = rb_ary_tmp_new(0);
 	    th->async_errinfo_queue_checked = 0;
-	    th->async_errinfo_mask_stack = rb_ary_new();
+	    th->async_errinfo_mask_stack = rb_ary_tmp_new(0);
+	    RBASIC(th->async_errinfo_mask_stack)->klass = 0;
 	}
     }