diff --git a/hw/pci-host/pnv_phb3.c b/hw/pci-host/pnv_phb3.c
index 947efa77dc98557fc33802be3ab6286b23d98803..bdc128013e67d87de2add1dfae0d6ec1bb678a92 100644
--- a/hw/pci-host/pnv_phb3.c
+++ b/hw/pci-host/pnv_phb3.c
@@ -1130,6 +1130,7 @@ static void pnv_phb3_root_bus_class_init(ObjectClass *klass, void *data)
 static const TypeInfo pnv_phb3_root_bus_info = {
     .name = TYPE_PNV_PHB3_ROOT_BUS,
     .parent = TYPE_PCIE_BUS,
+    .instance_size = sizeof(PnvPHB3RootBus),
     .class_init = pnv_phb3_root_bus_class_init,
     .interfaces = (InterfaceInfo[]) {
         { INTERFACE_PCIE_DEVICE },
diff --git a/hw/pci-host/pnv_phb4.c b/hw/pci-host/pnv_phb4.c
index 4e17a48d35b701d19a687bfde2945cefc7e10e19..9f115da7ac47d05258d655bda9ec29d3bf99dde9 100644
--- a/hw/pci-host/pnv_phb4.c
+++ b/hw/pci-host/pnv_phb4.c
@@ -1321,6 +1321,7 @@ static void pnv_phb4_root_bus_class_init(ObjectClass *klass, void *data)
 static const TypeInfo pnv_phb4_root_bus_info = {
     .name = TYPE_PNV_PHB4_ROOT_BUS,
     .parent = TYPE_PCIE_BUS,
+    .instance_size = sizeof(PnvPHB4RootBus),
     .class_init = pnv_phb4_root_bus_class_init,
     .interfaces = (InterfaceInfo[]) {
         { INTERFACE_PCIE_DEVICE },