diff --git a/sys/dev/netif/ix/ixgbe_dcb_82599.c b/sys/dev/netif/ix/ixgbe_dcb_82599.c
--- a/sys/dev/netif/ix/ixgbe_dcb_82599.c
+++ b/sys/dev/netif/ix/ixgbe_dcb_82599.c
@@ -322,6 +322,8 @@
 		if (map[i] > max_tc)
 			max_tc = map[i];
 	}
+	if (max_tc >= IXGBE_DCB_MAX_TRAFFIC_CLASS)
+		max_tc = IXGBE_DCB_MAX_TRAFFIC_CLASS - 1;
 
 
 	/* Configure PFC Tx thresholds per TC */