diff --git a/arch/x86/pci/mmconfig_32.c b/arch/x86/pci/mmconfig_32.c
index f10a7e9..8c19df8 100644
--- a/arch/x86/pci/mmconfig_32.c
+++ b/arch/x86/pci/mmconfig_32.c
@@ -47,7 +47,7 @@
  */
 static void pci_exp_set_dev_base(unsigned int base, int bus, int devfn)
 {
-	u32 dev_base = base | (bus << 20) | (devfn << 12);
+	u32 dev_base = base | PCI_MMCFG_BUS_OFFSET(bus) | (devfn << 12);
 	int cpu = smp_processor_id();
 	if (dev_base != mmcfg_last_accessed_device ||
 	    cpu != mmcfg_last_accessed_cpu) {