diff --git a/ChangeLog b/ChangeLog
index 503a24fc17..de5d713840 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Fri Jul 31 16:28:33 2009  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* io.c (rb_stdio_set_default_encoding): added.
+
+	* ruby.c (process_options): call rb_stdio_set_default_encoding
+	  after setting defualt internal and external.
+
 Fri Jul 31 15:06:33 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* tool/compile_prelude.rb: too long string literal causes compile error
diff --git a/io.c b/io.c
index fd0552b237..3153ff7c23 100644
--- a/io.c
+++ b/io.c
@@ -8407,6 +8407,17 @@ rb_io_set_encoding(int argc, VALUE *argv, VALUE io)
     return io;
 }
 
+void
+rb_stdio_set_default_encoding()
+{
+    extern VALUE rb_stdin, rb_stdout, rb_stderr;
+    VALUE val = Qnil;
+
+    rb_io_set_encoding(1, &val, rb_stdin);
+    rb_io_set_encoding(1, &val, rb_stdout);
+    rb_io_set_encoding(1, &val, rb_stderr);
+}
+
 static VALUE
 argf_external_encoding(VALUE argf)
 {
diff --git a/ruby.c b/ruby.c
index 180455e92d..6839bfe323 100644
--- a/ruby.c
+++ b/ruby.c
@@ -1399,6 +1399,7 @@ process_options(int argc, char **argv, struct cmdline_options *opt)
     else if (!rb_default_internal_encoding())
 	/* Freeze default_internal */
 	rb_enc_set_default_internal(Qnil);
+    rb_stdio_set_default_encoding();
 
     if (!tree) return Qfalse;