diff --git a/sys/alpha/pci/mcpcia_pci.c b/sys/alpha/pci/mcpcia_pci.c
index 870dcd6aa61c..cbcf934211cf 100644
--- a/sys/alpha/pci/mcpcia_pci.c
+++ b/sys/alpha/pci/mcpcia_pci.c
@@ -41,7 +41,7 @@ static int
 mcpcia_pcib_probe(device_t dev)
 {
 	device_set_desc(dev, "MCPCIA PCI host bus adapter");
-	device_add_child(dev, "pci", -1);
+	device_add_child(dev, "pci", device_get_unit(dev) << 4);
 	return (0);
 }