diff --git a/net/ipfw3_nat/ip_fw3_nat.c b/net/ipfw3_nat/ip_fw3_nat.c
--- a/net/ipfw3_nat/ip_fw3_nat.c
+++ b/net/ipfw3_nat/ip_fw3_nat.c
@@ -986,7 +986,7 @@
 			for (i = 0; i < ALIAS_RANGE; i++) {
 				s2 = a1->udp_in[i];
 				if (s2 != NULL) {
-					if (time_uptime - s2->timestamp > sysctl_var_icmp_timeout) {
+					if (time_uptime - s2->timestamp > sysctl_var_udp_timeout) {
 						a1->udp_in[i] = NULL;
 						kfree(s2, M_IPFW3_NAT);
 					}