diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
index 8bffdcb99a3d..c2e6ec257a28 100644
--- a/drivers/net/dsa/realtek/rtl8365mb.c
+++ b/drivers/net/dsa/realtek/rtl8365mb.c
@@ -1968,7 +1968,7 @@ static int rtl8365mb_detect(struct realtek_priv *priv)
 		mb->priv = priv;
 		mb->chip_id = chip_id;
 		mb->chip_ver = chip_ver;
-		mb->port_mask = BIT(priv->num_ports) - 1;
+		mb->port_mask = GENMASK(priv->num_ports - 1, 0);
 		mb->learn_limit_max = RTL8365MB_LEARN_LIMIT_MAX_8365MB_VC;
 		mb->jam_table = rtl8365mb_init_jam_8365mb_vc;
 		mb->jam_size = ARRAY_SIZE(rtl8365mb_init_jam_8365mb_vc);