diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 3dc00f0..6186f4d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -411,7 +411,7 @@
 {
 	struct pci_bus *child;
 	int is_cardbus = (dev->hdr_type == PCI_HEADER_TYPE_CARDBUS);
-	u32 buses;
+	u32 buses, i;
 	u16 bctl;
 
 	pci_read_config_dword(dev, PCI_PRIMARY_BUS, &buses);
@@ -470,6 +470,10 @@
 		/* Clear errors */
 		pci_write_config_word(dev, PCI_STATUS, 0xffff);
 
+		/* Prevent assigning a bus number that already exists.
+		 * This can happen when a bridge is hot-plugged */
+		if (pci_find_bus(pci_domain_nr(bus), max+1))
+			return max;
 		child = pci_alloc_child_bus(bus, dev, ++max);
 		buses = (buses & 0xff000000)
 		      | ((unsigned int)(child->primary)     <<  0)
@@ -501,7 +505,11 @@
 			 * as cards with a PCI-to-PCI bridge can be
 			 * inserted later.
 			 */
-			max += CARDBUS_RESERVE_BUSNR;
+			for (i=0; i<CARDBUS_RESERVE_BUSNR; i++)
+				if (pci_find_bus(pci_domain_nr(bus),
+							max+i+1))
+					break;
+			max += i;
 		}
 		/*
 		 * Set the subordinate bus number to its real value.