diff --git a/ChangeLog b/ChangeLog
index 9e510835b4..31cc4804b5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Oct 29 04:40:36 2009  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* io.c (Init_IO): rb_default_rs should be US-ASCII.
+
 Thu Oct 29 01:22:01 2009  Yutaka Kanemoto  <kanemoto@ruby-lang.org>
 
 	* ext/socket/extconf.rb : Compilation failure on AIX.
diff --git a/io.c b/io.c
index 1488dc1ecc..f04540417e 100644
--- a/io.c
+++ b/io.c
@@ -9692,7 +9692,7 @@ Init_IO(void)
     rb_output_fs = Qnil;
     rb_define_hooked_variable("$,", &rb_output_fs, 0, rb_str_setter);
 
-    rb_rs = rb_default_rs = rb_str_new2("\n");
+    rb_rs = rb_default_rs = rb_usascii_str_new2("\n");
     rb_gc_register_mark_object(rb_default_rs);
     rb_output_rs = Qnil;
     OBJ_FREEZE(rb_default_rs);	/* avoid modifying RS_default */