Index: sys/net/if_lagg.c
===================================================================
--- sys/net/if_lagg.c
+++ sys/net/if_lagg.c
@@ -1464,8 +1464,31 @@
 		break;
 
 	case SIOCSIFMTU:
-		/* Do not allow the MTU to be directly changed */
-		error = EINVAL;
+		LAGG_XLOCK(sc);
+		CK_SLIST_FOREACH(lp, &sc->sc_ports, lp_entries) {
+			if (lp->lp_ioctl != NULL)
+				error = (*lp->lp_ioctl)(lp->lp_ifp, cmd, data);
+			else
+				error = EINVAL;
+			if (error != 0) {
+				if_printf(ifp,
+				    "failed to change MTU to %d on port %s, "
+				    "reverting all ports to original MTU (%d)\n",
+				    ifr->ifr_mtu, lp->lp_ifp->if_xname, ifp->if_mtu);
+				break;
+			}
+		}
+		if (error == 0) {
+			ifp->if_mtu = ifr->ifr_mtu;
+		} else {
+			/* set every port back to the original MTU */
+			ifr->ifr_mtu = ifp->if_mtu;
+			CK_SLIST_FOREACH(lp, &sc->sc_ports, lp_entries) {
+				if (lp->lp_ioctl != NULL)
+					(*lp->lp_ioctl)(lp->lp_ifp, cmd, data);
+			}
+		}
+		LAGG_XUNLOCK(sc);
 		break;
 
 	default: