diff --git a/usr.sbin/cron/cron/popen.c b/usr.sbin/cron/cron/popen.c
index 3cd0f9aca9f2..e0861f5614b2 100644
--- a/usr.sbin/cron/cron/popen.c
+++ b/usr.sbin/cron/cron/popen.c
@@ -80,6 +80,7 @@ cron_popen(program, type)
 	for (argc = 0, cp = program; argc < MAX_ARGS; cp = NULL)
 		if (!(argv[argc++] = strtok(cp, " \t\n")))
 			break;
+	argv[MAX_ARGS] = NULL;
 
 #if WANT_GLOBBING
 	/* glob each piece */