diff --git a/ChangeLog b/ChangeLog
index 73fd7f7a30..ed7fe6f6f5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Jun  1 17:26:24 2001  K.Kosako  <kosako@sofnec.co.jp>
+
+	* hash.c (replace_i): ignore when key == Qundef.
+
 Fri Jun  1 16:50:59 2001  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* parse.y (call_args2): confusion with list_append() and
diff --git a/hash.c b/hash.c
index 7a08b0d500..2d99df3ce0 100644
--- a/hash.c
+++ b/hash.c
@@ -510,7 +510,10 @@ static int
 replace_i(key, val, hash)
     VALUE key, val, hash;
 {
-    rb_hash_aset(hash, key, val);
+    if (key != Qundef) {
+	rb_hash_aset(hash, key, val);
+    }
+
     return ST_CONTINUE;
 }