diff --git a/ChangeLog b/ChangeLog
index f879970fc8..70b08e0172 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,9 @@ Fri Dec 21 13:10:57 2007  Yukihiro Matsumoto  <matz@ruby-lang.org>
 	* encoding.c (rb_enc_from_encoding): returns Qnil for NULL
 	  encoding.
 
+	* io.c (rb_io_external_encoding): should fill delayed
+	  initialization for STDIN.
+
 Fri Dec 21 13:09:11 2007  Tanaka Akira  <akr@fsij.org>
 
 	* encoding.c (rb_locale_charmap): return nil if no locale information.
diff --git a/io.c b/io.c
index 6947987ee8..b03dac5e94 100644
--- a/io.c
+++ b/io.c
@@ -5671,6 +5671,9 @@ rb_io_external_encoding(VALUE io)
     rb_io_t *fptr;
 
     GetOpenFile(io, fptr);
+    if (!fptr->enc && fptr->fd == 0) {
+	fptr->enc = rb_default_external_encoding();
+    }
     return rb_enc_from_encoding(fptr->enc);
 }