diff --git a/Include/osdefs.h b/Include/osdefs.h
index 594fc107cf0..1a00fc0c6b2 100644
--- a/Include/osdefs.h
+++ b/Include/osdefs.h
@@ -46,7 +46,7 @@ PERFORMANCE OF THIS SOFTWARE.
 
 /* Mod by chrish: QNX has WATCOM, but isn't DOS */
 #if !defined(__QNX__)
-#if defined(MS_WINDOWS) || defined(__BORLANDC__) || defined(__WATCOMC__) || defined(__DJGPP__) || defined(__TOS_OS2__)
+#if defined(MS_WINDOWS) || defined(__BORLANDC__) || defined(__WATCOMC__) || defined(__DJGPP__) || defined(PYOS_OS2)
 #define SEP '\\'
 #define ALTSEP '/'
 #define MAXPATHLEN 256