1 files changed, 1 insertions, 1 deletions
diff --git a/io.c b/io.c
index 9a5ef85845..075644abeb 100644
--- a/io.c
+++ b/io.c
@@ -1133,7 +1133,7 @@ VALUE
 rb_io_binmode(io)
     VALUE io;
 {
-#if defined(NT) || defined(DJGPP) || defined(__CYGWIN__) || defined(__human68k__) || defined(__EMX__)
+#if defined _IOBIN || defined O_BINARY
     OpenFile *fptr;
 
     GetOpenFile(io, fptr);