diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index 34316f30f67d..f718c8ab2c8e 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: if_ethersubr.c,v 1.234 2017/01/10 05:42:34 ozaki-r Exp $	*/
+/*	$NetBSD: if_ethersubr.c,v 1.235 2017/01/13 06:11:56 msaitoh Exp $	*/
 
 /*
  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
@@ -61,7 +61,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_ethersubr.c,v 1.234 2017/01/10 05:42:34 ozaki-r Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_ethersubr.c,v 1.235 2017/01/13 06:11:56 msaitoh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_inet.h"
@@ -1475,10 +1475,6 @@ ether_enable_vlan_mtu(struct ifnet *ifp)
 	int error;
 	struct ethercom *ec = (void *)ifp;
 
-	/* Already have VLAN's do nothing. */
-	if (ec->ec_nvlans != 0)
-		return 0;
-
 	/* Parent does not support VLAN's */
 	if ((ec->ec_capabilities & ETHERCAP_VLAN_MTU) == 0)
 		return -1;
diff --git a/sys/net/if_vlan.c b/sys/net/if_vlan.c
index 017dab7d9dbf..99f7b2154929 100644
--- a/sys/net/if_vlan.c
+++ b/sys/net/if_vlan.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: if_vlan.c,v 1.93 2016/12/15 09:28:06 ozaki-r Exp $	*/
+/*	$NetBSD: if_vlan.c,v 1.94 2017/01/13 06:11:56 msaitoh Exp $	*/
 
 /*-
  * Copyright (c) 2000, 2001 The NetBSD Foundation, Inc.
@@ -78,7 +78,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_vlan.c,v 1.93 2016/12/15 09:28:06 ozaki-r Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_vlan.c,v 1.94 2017/01/13 06:11:56 msaitoh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_inet.h"
@@ -313,10 +313,12 @@ vlan_config(struct ifvlan *ifv, struct ifnet *p)
 		ifv->ifv_encaplen = ETHER_VLAN_ENCAP_LEN;
 		ifv->ifv_mintu = ETHERMIN;
 
-		if (ec->ec_nvlans == 0) {
+		if (ec->ec_nvlans++ == 0) {
 			if ((error = ether_enable_vlan_mtu(p)) >= 0) {
-				if (error)
+				if (error) {
+					ec->ec_nvlans--;
 					return error;
+				}
 				ifv->ifv_mtufudge = 0;
 			} else {
 				/*
@@ -329,7 +331,6 @@ vlan_config(struct ifvlan *ifv, struct ifnet *p)
 				ifv->ifv_mtufudge = ifv->ifv_encaplen;
 			}
 		}
-		ec->ec_nvlans++;
 
 		/*
 		 * If the parent interface can do hardware-assisted