diff --git a/lib/getopt.h b/lib/getopt.h
index fb30719..c4519b7 100644
--- a/lib/getopt.h
+++ b/lib/getopt.h
@@ -105,7 +105,7 @@
    errors, only prototype getopt for the GNU C library.  */
 extern int getopt (int argc, char *const *argv, const char *shortopts);
 #else /* not __GNU_LIBRARY__ */
-extern int getopt ();
+extern int getopt (void);
 #endif /* __GNU_LIBRARY__ */
 extern int getopt_long (int argc, char *const *argv, const char *shortopts,
 		        const struct option *longopts, int *longind);