diff --git a/ChangeLog b/ChangeLog
index 02eaf07770..14b3887de2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jul 16 18:30:20 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* hash.c (rb_hash_aset, recursive_hash): rejects recursive hash.
+	  [ruby-core:22921]
+
 Thu Jul 16 18:28:09 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* id.c (Init_id), vm.c (vm_exec): @#__ThrowState__ is no longer
diff --git a/hash.c b/hash.c
index c65d24263e..da47b55bea 100644
--- a/hash.c
+++ b/hash.c
@@ -1016,6 +1016,9 @@ VALUE
 rb_hash_aset(VALUE hash, VALUE key, VALUE val)
 {
     rb_hash_modify(hash);
+    if (hash == key) {
+	rb_raise(rb_eArgError, "recursive key for hash");
+    }
     if (RHASH(hash)->ntbl->type == &identhash || rb_obj_class(key) != rb_cString) {
 	st_insert(RHASH(hash)->ntbl, key, val);
     }
@@ -1546,7 +1549,7 @@ recursive_hash(VALUE hash, VALUE dummy, int recur)
     VALUE hval;
 
     if (recur) {
-	return LONG2FIX(0);
+	rb_raise(rb_eArgError, "recursive key for hash");
     }
     if (!RHASH(hash)->ntbl)
         return LONG2FIX(0);