diff --git a/src/modesel.c b/src/modesel.c
--- src/modesel.c
+++ src/modesel.c
@@ -6,6 +6,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include "zgv_io.h"
 #include "readnbkey.h"
 #include "modesel.h"