diff --git a/hw/pci.c b/hw/pci.c
index 2fed66f0a1..6035c890a8 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -494,7 +494,7 @@ PIIX3State *piix3_state;
 static inline int pci_slot_get_pirq(PCIDevice *pci_dev, int irq_num)
 {
     int slot_addend;
-    slot_addend = (pci_dev->devfn >> 3);
+    slot_addend = (pci_dev->devfn >> 3) - 1;
     return (irq_num + slot_addend) & 3;
 }