diff --git a/src/os_msdos.h b/src/os_msdos.h
index b8e90e1..49420a8 100644
--- a/src/os_msdos.h
+++ b/src/os_msdos.h
@@ -21,6 +21,7 @@
 # define USE_LONG_FNAME _USE_LFN    /* decide at run time */
 # define USE_FNAME_CASE
 # define HAVE_PUTENV
+# define HAVE_STDARG_H
 #else
 # define SHORT_FNAME		/* always 8.3 file name */
 #endif