diff --git a/hw/prep_pci.c b/hw/prep_pci.c
index f384e4215409d98ec829263e0c181f1c83a14f9b..6d6a1349cbe2ea0ef81fe909220135270a053716 100644
--- a/hw/prep_pci.c
+++ b/hw/prep_pci.c
@@ -135,7 +135,7 @@ PCIBus *pci_prep_init(qemu_irq *pic)
     int PPC_io_memory;
 
     s = qemu_mallocz(sizeof(PREPPCIState));
-    s->bus = pci_register_bus(prep_set_irq, prep_map_irq, pic, 0, 2);
+    s->bus = pci_register_bus(prep_set_irq, prep_map_irq, pic, 0, 4);
 
     register_ioport_write(0xcf8, 4, 4, pci_prep_addr_writel, s);
     register_ioport_read(0xcf8, 4, 4, pci_prep_addr_readl, s);