diff --git a/ChangeLog b/ChangeLog
index 15232de515..57e4b407cb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,4 @@
-Fri Dec  7 12:27:18 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Fri Dec  7 15:04:01 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* array.c (flatten): some performance improvements, based on a patch
 	  from Yusuke ENDOH <mame AT tsg.ne.jp> in [ruby-core:13877].
@@ -7,6 +7,8 @@ Fri Dec  7 12:27:18 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 	* thread.c (rb_exec_recursive): use Hash instead of Array for
 	  performance improvement.  [ruby-core:13898]
 
+	* thread.c (recursive_pop): use object ID.
+
 Thu Dec  6 19:52:50 2007  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* parse.y (arg): typo fixed ("!" -> "|") in the ripper code.
diff --git a/thread.c b/thread.c
index b6b827f9bd..94d2ae5f49 100644
--- a/thread.c
+++ b/thread.c
@@ -2593,7 +2593,7 @@ recursive_check(VALUE hash, VALUE obj)
 
 	if (NIL_P(list) || TYPE(list) != T_HASH)
 	    return Qfalse;
-	if (NIL_P(rb_hash_lookup(list, rb_obj_id(obj))))
+	if (NIL_P(rb_hash_lookup(list, obj)))
 	    return Qfalse;
 	return Qtrue;
     }
@@ -2617,7 +2617,7 @@ recursive_push(VALUE hash, VALUE obj)
 	list = rb_hash_new();
 	rb_hash_aset(hash, sym, list);
     }
-    rb_hash_aset(list, rb_obj_id(obj), Qtrue);
+    rb_hash_aset(list, obj, Qtrue);
     return hash;
 }
 
@@ -2650,21 +2650,22 @@ VALUE
 rb_exec_recursive(VALUE (*func) (VALUE, VALUE, int), VALUE obj, VALUE arg)
 {
     VALUE hash = rb_thread_local_aref(rb_thread_current(), recursive_key);
+    VALUE objid = rb_obj_id(obj);
 
-    if (recursive_check(hash, obj)) {
+    if (recursive_check(hash, objid)) {
 	return (*func) (obj, arg, Qtrue);
     }
     else {
 	VALUE result = Qundef;
 	int state;
 
-	hash = recursive_push(hash, obj);
+	hash = recursive_push(hash, objid);
 	PUSH_TAG();
 	if ((state = EXEC_TAG()) == 0) {
 	    result = (*func) (obj, arg, Qfalse);
 	}
 	POP_TAG();
-	recursive_pop(hash, obj);
+	recursive_pop(hash, objid);
 	if (state)
 	    JUMP_TAG(state);
 	return result;