diff --git a/ChangeLog b/ChangeLog
index f08d12160c..d2fb1041d3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Feb 25 10:16:50 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* rubyio.h (HAVE_RB_IO_T): macro to tell if rb_io_t is defined.
+
 Sat Feb 24 19:39:16 2007  Minero Aoki  <aamine@loveruby.net>
 
 	* common.mk: new target "btest", to run bootstraptests.
diff --git a/rubyio.h b/rubyio.h
index 144fc6cd4b..14d2039183 100644
--- a/rubyio.h
+++ b/rubyio.h
@@ -39,6 +39,8 @@ typedef struct rb_io_t {
     int rbuf_capa;
 } rb_io_t;
 
+#define HAVE_RB_IO_T 1
+
 #define FMODE_READABLE  1
 #define FMODE_WRITABLE  2
 #define FMODE_READWRITE 3