diff --git a/ChangeLog b/ChangeLog
index a7f4de32a0..3bc621bd86 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Mar  4 19:10:43 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* hash.c (rb_hash_aset): should not copy key string when
+	  compare_by_identity is set.  [ruby-dev:33604]
+
 Tue Mar  4 16:29:06 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* parse.y (parser_yylex): disallow non digits '0o' expression.
diff --git a/hash.c b/hash.c
index eca3e5c6a2..3b74b8c20b 100644
--- a/hash.c
+++ b/hash.c
@@ -103,6 +103,11 @@ static const struct st_hash_type objhash = {
     rb_any_hash,
 };
 
+static const struct st_hash_type identhash = {
+    st_numcmp,
+    st_numhash,
+};
+
 typedef int st_foreach_func(st_data_t, st_data_t, st_data_t);
 
 struct foreach_safe_arg {
@@ -932,7 +937,8 @@ VALUE
 rb_hash_aset(VALUE hash, VALUE key, VALUE val)
 {
     rb_hash_modify(hash);
-    if (TYPE(key) != T_STRING || st_lookup(RHASH(hash)->ntbl, key, 0)) {
+    if (RHASH(hash)->ntbl->type == &identhash ||
+	TYPE(key) != T_STRING || st_lookup(RHASH(hash)->ntbl, key, 0)) {
 	st_insert(RHASH(hash)->ntbl, key, val);
     }
     else {
@@ -1685,11 +1691,6 @@ rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
     return ary;
 }
 
-static const struct st_hash_type identhash = {
-    st_numcmp,
-    st_numhash,
-};
-
 /*
  *  call-seq:
  *     hsh.compare_by_identity => hsh