diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 0e60270297..8feb3451a0 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -1237,6 +1237,7 @@ static const TypeInfo virtio_ccw_bus_info = {
     .name = TYPE_VIRTIO_CCW_BUS,
     .parent = TYPE_VIRTIO_BUS,
     .instance_size = sizeof(VirtioCcwBusState),
+    .class_size = sizeof(VirtioCcwBusClass),
     .class_init = virtio_ccw_bus_class_init,
 };
 
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index fc69570dcc..5bc769f685 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -2133,6 +2133,7 @@ static const TypeInfo virtio_pci_bus_info = {
     .name          = TYPE_VIRTIO_PCI_BUS,
     .parent        = TYPE_VIRTIO_BUS,
     .instance_size = sizeof(VirtioPCIBusState),
+    .class_size    = sizeof(VirtioPCIBusClass),
     .class_init    = virtio_pci_bus_class_init,
 };