diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
index 26390863d6..fa05844319 100644
--- a/hw/pci-host/q35.c
+++ b/hw/pci-host/q35.c
@@ -50,10 +50,12 @@ static void q35_host_realize(DeviceState *dev, Error **errp)
     Q35PCIHost *s = Q35_HOST_DEVICE(dev);
     SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
 
-    sysbus_add_io(sbd, MCH_HOST_BRIDGE_CONFIG_ADDR, &pci->conf_mem);
+    memory_region_add_subregion(s->mch.address_space_io,
+                                MCH_HOST_BRIDGE_CONFIG_ADDR, &pci->conf_mem);
     sysbus_init_ioports(sbd, MCH_HOST_BRIDGE_CONFIG_ADDR, 4);
 
-    sysbus_add_io(sbd, MCH_HOST_BRIDGE_CONFIG_DATA, &pci->data_mem);
+    memory_region_add_subregion(s->mch.address_space_io,
+                                MCH_HOST_BRIDGE_CONFIG_DATA, &pci->data_mem);
     sysbus_init_ioports(sbd, MCH_HOST_BRIDGE_CONFIG_DATA, 4);
 
     /* register q35 0xcf8 port as coalesced pio */