diff --git a/ChangeLog b/ChangeLog
index ca520dcbe2..1918cc2295 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Aug 20 14:49:42 2004  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* io.c (rb_io_check_writable): no need to check read buffer if
+	  already changed to write mode.
+
 Fri Aug 20 11:46:43 2004  UENO Katsuhiro  <katsu@blue.sky.or.jp>
 
 	* ext/zlib/zlib.c: GzipReader#ungetc caused crc error.
diff --git a/io.c b/io.c
index d64e41d683..45056040bb 100644
--- a/io.c
+++ b/io.c
@@ -254,7 +254,7 @@ rb_io_check_writable(fptr)
     if (!(fptr->mode & FMODE_WRITABLE)) {
 	rb_raise(rb_eIOError, "not opened for writing");
     }
-    if (READ_DATA_BUFFERED(fptr->f)) {
+    if ((fptr->mode & FMODE_RBUF) && READ_DATA_BUFFERED(fptr->f)) {
 	rb_warn("read buffer data lost");
     }
 #if NEED_IO_SEEK_BETWEEN_RW