diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index b48047f50c..bb3b10557f 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -47,6 +47,7 @@
 #include "hw/sysbus.h"
 #include "hw/i2c/smbus_eeprom.h"
 #include "hw/xen/xen-x86.h"
+#include "hw/xen/xen.h"
 #include "exec/memory.h"
 #include "hw/acpi/acpi.h"
 #include "hw/acpi/piix4.h"
@@ -73,6 +74,17 @@ static const int ide_iobase2[MAX_IDE_BUS] = { 0x3f6, 0x376 };
 static const int ide_irq[MAX_IDE_BUS] = { 14, 15 };
 #endif
 
+/*
+ * Return the global irq number corresponding to a given device irq
+ * pin. We could also use the bus number to have a more precise mapping.
+ */
+static int pc_pci_slot_get_pirq(PCIDevice *pci_dev, int pci_intx)
+{
+    int slot_addend;
+    slot_addend = PCI_SLOT(pci_dev->devfn) - 1;
+    return (pci_intx + slot_addend) & 3;
+}
+
 /* PC hardware initialisation */
 static void pc_init1(MachineState *machine,
                      const char *host_type, const char *pci_type)
@@ -216,6 +228,9 @@ static void pc_init1(MachineState *machine,
                               x86ms->below_4g_mem_size,
                               x86ms->above_4g_mem_size,
                               pci_memory, ram_memory);
+        pci_bus_map_irqs(pci_bus,
+                         xen_enabled() ? xen_pci_slot_get_pirq
+                                       : pc_pci_slot_get_pirq);
         pcms->bus = pci_bus;
 
         pci_dev = pci_create_simple_multifunction(pci_bus, -1, true, type);
diff --git a/hw/isa/piix3.c b/hw/isa/piix3.c
index 666e794f77..283b971ec4 100644
--- a/hw/isa/piix3.c
+++ b/hw/isa/piix3.c
@@ -79,17 +79,6 @@ static void piix3_set_irq(void *opaque, int pirq, int level)
     piix3_set_irq_level(piix3, pirq, level);
 }
 
-/*
- * Return the global irq number corresponding to a given device irq
- * pin. We could also use the bus number to have a more precise mapping.
- */
-static int pci_slot_get_pirq(PCIDevice *pci_dev, int pci_intx)
-{
-    int slot_addend;
-    slot_addend = PCI_SLOT(pci_dev->devfn) - 1;
-    return (pci_intx + slot_addend) & 3;
-}
-
 static PCIINTxRoute piix3_route_intx_pin_to_irq(void *opaque, int pin)
 {
     PIIX3State *piix3 = opaque;
@@ -385,7 +374,6 @@ static void piix3_realize(PCIDevice *dev, Error **errp)
     }
 
     pci_bus_irqs(pci_bus, piix3_set_irq, piix3, PIIX_NUM_PIRQS);
-    pci_bus_map_irqs(pci_bus, pci_slot_get_pirq);
     pci_bus_set_route_irq_fn(pci_bus, piix3_route_intx_pin_to_irq);
 }
 
@@ -421,7 +409,6 @@ static void piix3_xen_realize(PCIDevice *dev, Error **errp)
      * These additional routes can be discovered through ACPI.
      */
     pci_bus_irqs(pci_bus, xen_piix3_set_irq, piix3, XEN_PIIX_NUM_PIRQS);
-    pci_bus_map_irqs(pci_bus, xen_pci_slot_get_pirq);
 }
 
 static void piix3_xen_class_init(ObjectClass *klass, void *data)