diff --git a/drivers/net/dsa/sja1105/sja1105_mdio.c b/drivers/net/dsa/sja1105/sja1105_mdio.c
index 215dd17ca790..4059fcc8c832 100644
--- a/drivers/net/dsa/sja1105/sja1105_mdio.c
+++ b/drivers/net/dsa/sja1105/sja1105_mdio.c
@@ -256,6 +256,9 @@ static int sja1105_base_tx_mdio_read(struct mii_bus *bus, int phy, int reg)
 	u32 tmp;
 	int rc;
 
+	if (reg & MII_ADDR_C45)
+		return -EOPNOTSUPP;
+
 	rc = sja1105_xfer_u32(priv, SPI_READ, regs->mdio_100base_tx + reg,
 			      &tmp, NULL);
 	if (rc < 0)
@@ -272,6 +275,9 @@ static int sja1105_base_tx_mdio_write(struct mii_bus *bus, int phy, int reg,
 	const struct sja1105_regs *regs = priv->info->regs;
 	u32 tmp = val;
 
+	if (reg & MII_ADDR_C45)
+		return -EOPNOTSUPP;
+
 	return sja1105_xfer_u32(priv, SPI_WRITE, regs->mdio_100base_tx + reg,
 				&tmp, NULL);
 }