diff --git a/ChangeLog b/ChangeLog
index 98d27835c4..026fd56531 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Apr  8 19:03:33 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (rb_io_binmode): inverted condition.  [ruby-dev:23349]
+
 Thu Apr  8 18:22:00 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/iconv/iconv.c (iconv_s_list): return encoding list if no block
diff --git a/io.c b/io.c
index 3ddf904b96..6312de8c9c 100644
--- a/io.c
+++ b/io.c
@@ -2150,7 +2150,7 @@ rb_io_binmode(io)
     OpenFile *fptr;
 
     GetOpenFile(io, fptr);
-    if ((fptr->mode & FMODE_BINMODE) && READ_DATA_BUFFERED(fptr->f)) {
+    if (!(fptr->mode & FMODE_BINMODE) && READ_DATA_BUFFERED(fptr->f)) {
 	rb_raise(rb_eIOError, "buffer already filled with text-mode content");
     }
 #ifdef __human68k__