diff --git a/drivers/net/dsa/rtl8366rb.c b/drivers/net/dsa/rtl8366rb.c
index 01d794f94156b..6382404814c3d 100644
--- a/drivers/net/dsa/rtl8366rb.c
+++ b/drivers/net/dsa/rtl8366rb.c
@@ -1520,7 +1520,7 @@ static int rtl8366rb_set_mc_index(struct realtek_smi *smi, int port, int index)
 
 static bool rtl8366rb_is_vlan_valid(struct realtek_smi *smi, unsigned int vlan)
 {
-	unsigned int max = RTL8366RB_NUM_VLANS;
+	unsigned int max = RTL8366RB_NUM_VLANS - 1;
 
 	if (smi->vlan4k_enabled)
 		max = RTL8366RB_NUM_VIDS - 1;