diff --git a/sys/dev/cxgbe/t4_main.c b/sys/dev/cxgbe/t4_main.c
index 3e87eafe155..35fb17d4f71 100644
--- a/sys/dev/cxgbe/t4_main.c
+++ b/sys/dev/cxgbe/t4_main.c
@@ -3031,8 +3031,10 @@ update_mac_settings(struct ifnet *ifp, int flags)
 		TAILQ_FOREACH(ifma, &ifp->if_multiaddrs, ifma_link) {
 			if (ifma->ifma_addr->sa_family != AF_LINK)
 				continue;
-			mcaddr[i++] =
+			mcaddr[i] =
 			    LLADDR((struct sockaddr_dl *)ifma->ifma_addr);
+			MPASS(ETHER_IS_MULTICAST(mcaddr[i]));
+			i++;
 
 			if (i == FW_MAC_EXACT_CHUNK) {
 				rc = t4_alloc_mac_filt(sc, sc->mbox, viid, del,