diff --git a/hw/pci/pci_bridge.c b/hw/pci/pci_bridge.c
index edb8c8d9c9..bf93ac6ed1 100644
--- a/hw/pci/pci_bridge.c
+++ b/hw/pci/pci_bridge.c
@@ -366,7 +366,7 @@ int pci_bridge_initfn(PCIDevice *dev)
     qbus_create_inplace(&sec_bus->qbus, TYPE_PCI_BUS, &dev->qdev,
                         br->bus_name);
     sec_bus->parent_dev = dev;
-    sec_bus->map_irq = br->map_irq;
+    sec_bus->map_irq = br->map_irq ? br->map_irq : pci_swizzle_map_irq_fn;
     sec_bus->address_space_mem = &br->address_space_mem;
     memory_region_init(&br->address_space_mem, "pci_bridge_pci", INT64_MAX);
     sec_bus->address_space_io = &br->address_space_io;