diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -987,7 +987,8 @@
 	struct sockaddr_dl *sdl;
 
 	ifp->if_addrlen = ETHER_ADDR_LEN;
-	ifp->if_hdrlen = ETHER_HDR_LEN;
+	ifp->if_hdrlen = (ifp->if_capabilities & IFCAP_VLAN_MTU) != 0 ?
+	    ETHER_HDR_LEN + ETHER_VLAN_ENCAP_LEN : ETHER_HDR_LEN;
 	ifp->if_mtu = ETHERMTU;
 	if_attach(ifp);
 	ifp->if_output = ether_output;