diff --git a/hw/pci-bridge/pci_expander_bridge.c b/hw/pci-bridge/pci_expander_bridge.c
index e62de4218f..ca66bc721a 100644
--- a/hw/pci-bridge/pci_expander_bridge.c
+++ b/hw/pci-bridge/pci_expander_bridge.c
@@ -66,11 +66,6 @@ static int pxb_bus_num(PCIBus *bus)
     return pxb->bus_nr;
 }
 
-static bool pxb_is_root(PCIBus *bus)
-{
-    return true; /* by definition */
-}
-
 static uint16_t pxb_bus_numa_node(PCIBus *bus)
 {
     PXBDev *pxb = convert_to_pxb(bus->parent_dev);
@@ -83,7 +78,6 @@ static void pxb_bus_class_init(ObjectClass *class, void *data)
     PCIBusClass *pbc = PCI_BUS_CLASS(class);
 
     pbc->bus_num = pxb_bus_num;
-    pbc->is_root = pxb_is_root;
     pbc->numa_node = pxb_bus_numa_node;
 }
 
diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index a78023f669..b386777045 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -129,14 +129,9 @@ static void pci_bus_unrealize(BusState *qbus, Error **errp)
     vmstate_unregister(NULL, &vmstate_pcibus, bus);
 }
 
-static bool pcibus_is_root(PCIBus *bus)
-{
-    return !bus->parent_dev;
-}
-
 static int pcibus_num(PCIBus *bus)
 {
-    if (pcibus_is_root(bus)) {
+    if (pci_bus_is_root(bus)) {
         return 0; /* pci host bridge */
     }
     return bus->parent_dev->config[PCI_SECONDARY_BUS];
@@ -164,7 +159,6 @@ static void pci_bus_class_init(ObjectClass *klass, void *data)
     k->unrealize = pci_bus_unrealize;
     k->reset = pcibus_reset;
 
-    pbc->is_root = pcibus_is_root;
     pbc->bus_num = pcibus_num;
     pbc->numa_node = pcibus_numa_node;
     pbc->allows_extended_config_space = pcibus_allows_extended_config_space;
@@ -398,6 +392,7 @@ static void pci_root_bus_init(PCIBus *bus, DeviceState *parent,
     bus->slot_reserved_mask = 0x0;
     bus->address_space_mem = address_space_mem;
     bus->address_space_io = address_space_io;
+    bus->flags |= PCI_BUS_IS_ROOT;
 
     /* host bridge */
     QLIST_INIT(&bus->child);
@@ -415,11 +410,6 @@ bool pci_bus_is_express(PCIBus *bus)
     return object_dynamic_cast(OBJECT(bus), TYPE_PCIE_BUS);
 }
 
-bool pci_bus_is_root(PCIBus *bus)
-{
-    return PCI_BUS_GET_CLASS(bus)->is_root(bus);
-}
-
 bool pci_bus_allows_extended_config_space(PCIBus *bus)
 {
     return PCI_BUS_GET_CLASS(bus)->allows_extended_config_space(bus);
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 509c1ff555..9056cdfa3c 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -20,6 +20,7 @@
 #include "standard-headers/linux/virtio_pci.h"
 #include "hw/virtio/virtio.h"
 #include "hw/pci/pci.h"
+#include "hw/pci/pci_bus.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "hw/pci/msi.h"
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index fdd4c43d3a..edf44de21d 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -395,7 +395,6 @@ typedef PCIINTxRoute (*pci_route_irq_fn)(void *opaque, int pin);
 #define TYPE_PCIE_BUS "PCIE"
 
 bool pci_bus_is_express(PCIBus *bus);
-bool pci_bus_is_root(PCIBus *bus);
 bool pci_bus_allows_extended_config_space(PCIBus *bus);
 
 void pci_root_bus_new_inplace(PCIBus *bus, size_t bus_size, DeviceState *parent,
diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
index f6df834170..aea98d5040 100644
--- a/include/hw/pci/pci_bus.h
+++ b/include/hw/pci/pci_bus.h
@@ -15,14 +15,19 @@ typedef struct PCIBusClass {
     BusClass parent_class;
     /*< public >*/
 
-    bool (*is_root)(PCIBus *bus);
     int (*bus_num)(PCIBus *bus);
     uint16_t (*numa_node)(PCIBus *bus);
     bool (*allows_extended_config_space)(PCIBus *bus);
 } PCIBusClass;
 
+enum PCIBusFlags {
+    /* This bus is the root of a PCI domain */
+    PCI_BUS_IS_ROOT                                         = 0x0001,
+};
+
 struct PCIBus {
     BusState qbus;
+    enum PCIBusFlags flags;
     PCIIOMMUFunc iommu_fn;
     void *iommu_opaque;
     uint8_t devfn_min;
@@ -47,4 +52,9 @@ struct PCIBus {
     Notifier machine_done;
 };
 
+static inline bool pci_bus_is_root(PCIBus *bus)
+{
+    return !!(bus->flags & PCI_BUS_IS_ROOT);
+}
+
 #endif /* QEMU_PCI_BUS_H */