Index: sbin/ifconfig/carp.c
===================================================================
--- sbin/ifconfig/carp.c	(revision 349162)
+++ sbin/ifconfig/carp.c	(working copy)
@@ -161,7 +161,7 @@
 {
 
 	if (carpr_vhid == -1)
-		errx(1, "passwd requires vhid");
+		errx(1, "pass requires vhid (must come first)");
 
 	carpr_key = val;
 }
@@ -171,9 +171,14 @@
 {
 
 	if (carpr_vhid == -1)
-		errx(1, "advskew requires vhid");
+		errx(1, "advskew requires vhid (must come first)");
 
 	carpr_advskew = atoi(val);
+
+	if (carpr_advskew < 0 || carpr_advskew > CARP_MAXSKEW)
+		errx(1, "advskew must be something between 0 and %u",
+			CARP_MAXSKEW);
+
 }
 
 static void
@@ -181,9 +186,13 @@
 {
 
 	if (carpr_vhid == -1)
-		errx(1, "advbase requires vhid");
+		errx(1, "advbase requires vhid (must come first)");
 
 	carpr_advbase = atoi(val);
+
+	if (carpr_advbase < CARP_DFLTINTV || carpr_advbase > 255)
+		errx(1, "advbase must be greater than 0 and less than 256");
+
 }
 
 static void
@@ -192,7 +201,7 @@
 	int i;
 
 	if (carpr_vhid == -1)
-		errx(1, "state requires vhid");
+		errx(1, "state requires vhid (must come first)");
 
 	for (i = 0; i <= CARP_MAXSTATE; i++)
 		if (strcasecmp(carp_states[i], val) == 0) {
Index: sbin/ifconfig/ifconfig.8
===================================================================
--- sbin/ifconfig/ifconfig.8	(revision 349162)
+++ sbin/ifconfig/ifconfig.8	(working copy)
@@ -2841,7 +2841,7 @@
 Specifies the skew to add to the base advertisement interval to
 make one host advertise slower than another host.
 It is specified in 1/256 of seconds.
-The acceptable values are 1 to 254.
+The acceptable values are 0 to 240.
 The default value is 0.
 .It Cm pass Ar phrase
 Set the authentication key to
Index: sys/netinet/ip_carp.c
===================================================================
--- sys/netinet/ip_carp.c	(revision 349162)
+++ sys/netinet/ip_carp.c	(working copy)
@@ -1,4 +1,4 @@
-/*-
+*-
  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
  *
  * Copyright (c) 2002 Michael Shalayeff.
@@ -1766,15 +1766,14 @@
 		} else
 			CARP_LOCK(sc);
 		locked = 1;
-		if (carpr.carpr_advbase > 0) {
-			if (carpr.carpr_advbase > 255 ||
-			    carpr.carpr_advbase < CARP_DFLTINTV) {
-				error = EINVAL;
-				break;
-			}
-			sc->sc_advbase = carpr.carpr_advbase;
+		if (carpr.carpr_advbase < CARP_DFLTINTV ||
+		    carpr.carpr_advbase > 255) {
+			error = EINVAL;
+			break;
 		}
-		if (carpr.carpr_advskew >= 255) {
+		sc->sc_advbase = carpr.carpr_advbase;
+		if (carpr.carpr_advskew < 0 ||
+		    carpr.carpr_advskew > DEMOTE_ADVSKEW(sc)) {
 			error = EINVAL;
 			break;
 		}