diff --git a/ChangeLog b/ChangeLog
index 8e95318dbc..dac7aea01c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Thu Dec 18 17:00:56 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* hash.c (rb_hash_aset): string key copying only happen if key is
+	  an exact instance of String, not a subclass. based on a patch
+	  from Mike Gold <mike.gold.4433 at gmail.com> in [ruby-talk:322667].
+	  [incompatible] [ruby-talk:322417]
+
 Thu Dec 18 16:48:12 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* lib/optparse/version.rb: remove variable shadowing to stop
diff --git a/hash.c b/hash.c
index 044964c809..f3bd0b66b8 100644
--- a/hash.c
+++ b/hash.c
@@ -984,7 +984,7 @@ rb_hash_aset(VALUE hash, VALUE key, VALUE val)
 {
     rb_hash_modify(hash);
     if (RHASH(hash)->ntbl->type == &identhash ||
-	TYPE(key) != T_STRING || st_lookup(RHASH(hash)->ntbl, key, 0)) {
+	rb_obj_class(key) != rb_cString || st_lookup(RHASH(hash)->ntbl, key, 0)) {
 	st_insert(RHASH(hash)->ntbl, key, val);
     }
     else {