--- netkit-ftp-0.17/ftp/main.c	2005-02-11 09:19:35.000000000 +0100
+++ netkit-ftp-0.17/ftp/main.c.new	2005-02-11 09:19:01.000000000 +0100
@@ -259,6 +259,10 @@
 
 #ifdef USE_SSL
 			case 'z':
+				if (!optarg) {
+					fprintf(stderr, "ftp: the -z option requires an argument\n");
+					exit(1);
+				}
 				if (strcmp(optarg, "debug") == 0 ) {
 				    ssl_debug_flag=1;
 				}