diff --git a/hw/pci-host/pnv_phb3.c b/hw/pci-host/pnv_phb3.c
index af8575c007..9054c393a2 100644
--- a/hw/pci-host/pnv_phb3.c
+++ b/hw/pci-host/pnv_phb3.c
@@ -1169,6 +1169,7 @@ 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,
 };
 
diff --git a/hw/pci-host/pnv_phb4.c b/hw/pci-host/pnv_phb4.c
index 824e1a73fb..ccbde841fc 100644
--- a/hw/pci-host/pnv_phb4.c
+++ b/hw/pci-host/pnv_phb4.c
@@ -1773,6 +1773,7 @@ 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,
 };