diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 15a492261895..a51dfedf0014 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -49,7 +49,8 @@ void dsa_slave_mii_bus_init(struct dsa_switch *ds)
 	ds->slave_mii_bus->name = "dsa slave smi";
 	ds->slave_mii_bus->read = dsa_slave_phy_read;
 	ds->slave_mii_bus->write = dsa_slave_phy_write;
-	snprintf(ds->slave_mii_bus->id, MII_BUS_ID_SIZE, "dsa-%d", ds->index);
+	snprintf(ds->slave_mii_bus->id, MII_BUS_ID_SIZE, "dsa-%d.%d",
+		 ds->dst->tree, ds->index);
 	ds->slave_mii_bus->parent = ds->dev;
 	ds->slave_mii_bus->phy_mask = ~ds->phys_mii_mask;
 }