diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index e78b683f7305..825d840cdb8c 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -2353,9 +2353,8 @@ static int b53_switch_init(struct b53_device *dev)
 			dev->cpu_port = 5;
 	}
 
-	/* cpu port is always last */
-	dev->num_ports = dev->cpu_port + 1;
 	dev->enabled_ports |= BIT(dev->cpu_port);
+	dev->num_ports = fls(dev->enabled_ports);
 
 	/* Include non standard CPU port built-in PHYs to be probed */
 	if (is539x(dev) || is531x5(dev)) {