--- a/add-test/add_test.c
+++ b/add-test/add_test.c
@@ -9,6 +9,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "gsm.h"
 
@@ -29,7 +30,7 @@ word M_gsm_abs P((word op1));
 longword M_gsm_L_mult P((word op1, word op2));
 longword M_gsm_L_add P((longword op1, longword op2));
 
-help()
+void help(void)
 {
 puts( "  add a b      sub a b     mult a b   div    a b" );
 puts( "L_add A B    L_sub A B   L_mult A B   mult_r a b" );