diff --git a/sbin/ipfw/ipfw2.c b/sbin/ipfw/ipfw2.c
index 8ad8f90cc317..bc8af9f833a6 100644
--- a/sbin/ipfw/ipfw2.c
+++ b/sbin/ipfw/ipfw2.c
@@ -3625,7 +3625,7 @@ compile_rule(char *av[], uint32_t *rbuf, int *rbufsize, struct tidx *tstate)
 		action->opcode = O_NAT;
 		action->len = F_INSN_SIZE(ipfw_insn_nat);
 		CHECK_ACTLEN;
-		if (_substrcmp(*av, "global") == 0) {
+		if (*av != NULL && _substrcmp(*av, "global") == 0) {
 			action->arg1 = 0;
 			av++;
 			break;