diff --git a/arch/ia64/pci/pci.c b/arch/ia64/pci/pci.c
index d4e162d35b3467b9d7814769129237583f8cb100..7cc3be9fa7c65a0dd700dfd30c04cc7be822922d 100644
--- a/arch/ia64/pci/pci.c
+++ b/arch/ia64/pci/pci.c
@@ -478,9 +478,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 
 int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
-	struct pci_controller *controller = bridge->bus->sysdata;
-
-	ACPI_COMPANION_SET(&bridge->dev, controller->companion);
+	/*
+	 * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
+	 * here, pci_create_root_bus() has been called by someone else and
+	 * sysdata is likely to be different from what we expect.  Let it go in
+	 * that case.
+	 */
+	if (!bridge->dev.parent) {
+		struct pci_controller *controller = bridge->bus->sysdata;
+		ACPI_COMPANION_SET(&bridge->dev, controller->companion);
+	}
 	return 0;
 }
 
diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index d93963340c3c0d958385ce4ec8aadcdfe225a174..14a63ed6fe092cd3f512d155046942a28c3744e8 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -482,9 +482,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 
 int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
-	struct pci_sysdata *sd = bridge->bus->sysdata;
-
-	ACPI_COMPANION_SET(&bridge->dev, sd->companion);
+	/*
+	 * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
+	 * here, pci_create_root_bus() has been called by someone else and
+	 * sysdata is likely to be different from what we expect.  Let it go in
+	 * that case.
+	 */
+	if (!bridge->dev.parent) {
+		struct pci_sysdata *sd = bridge->bus->sysdata;
+		ACPI_COMPANION_SET(&bridge->dev, sd->companion);
+	}
 	return 0;
 }