diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index a9e64a8..67e41c1 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2298,6 +2298,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     mc->hot_add_cpu = pc_hot_add_cpu;
     mc->max_cpus = 255;
     mc->reset = pc_machine_reset;
+    machine_class_add_always_available_bus(mc, "sysbus", TYPE_SYSTEM_BUS);
     hc->pre_plug = pc_machine_device_pre_plug_cb;
     hc->plug = pc_machine_device_plug_cb;
     hc->unplug_request = pc_machine_device_unplug_request_cb;
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index a59bbb9..d0162a9 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -430,11 +430,26 @@ static void pc_xen_hvm_init(MachineState *machine)
 
 static void pc_i440fx_machine_options(MachineClass *m)
 {
+    MachineBusInfo *pci0;
+
     m->family = "pc_piix";
     m->desc = "Standard PC (i440FX + PIIX, 1996)";
     m->hot_add_cpu = pc_hot_add_cpu;
     m->default_machine_opts = "firmware=bios-256k.bin";
     m->default_display = "std";
+    pci0 = machine_class_add_always_available_bus(m, "pci.0", TYPE_PCI_BUS);
+
+    /* Sanity check to ensure we are reporting only legacy PCI devices as supported */
+    assert(pci0->accepted_device_types != NULL &&
+           pci0->accepted_device_types->next == NULL &&
+           !strcmp(pci0->accepted_device_types->value,
+                     INTERFACE_LEGACY_PCI_DEVICE));
+
+    machine_class_add_always_available_bus(m, "floppy-bus.0", "floppy-bus"); //FIXME: use macro
+    machine_class_add_always_available_bus(m, "i2c", "i2c-bus"); //FIXME: use macro
+    machine_class_add_always_available_bus(m, "isa.0", TYPE_ISA_BUS);
+    machine_class_add_always_available_bus(m, "ide.0", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.1", "IDE");//FIXME: use macro
 }
 
 static void pc_i440fx_2_8_machine_options(MachineClass *m)
@@ -1083,6 +1098,10 @@ static void isapc_machine_options(MachineClass *m)
     m->max_cpus = 1;
     m->option_rom_has_mr = true;
     m->rom_file_has_mr = false;
+    machine_class_add_always_available_bus(m, "floppy-bus.0", "floppy-bus"); //FIXME: use macro
+    machine_class_add_always_available_bus(m, "isa.0", TYPE_ISA_BUS);
+    machine_class_add_always_available_bus(m, "ide.0", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.1", "IDE");//FIXME: use macro
     pcmc->pci_enabled = false;
     pcmc->has_acpi_build = false;
     pcmc->smbios_defaults = false;
@@ -1102,6 +1121,12 @@ static void xenfv_machine_options(MachineClass *m)
     m->max_cpus = HVM_MAX_VCPUS;
     m->default_machine_opts = "accel=xen";
     m->hot_add_cpu = pc_hot_add_cpu;
+    machine_class_add_always_available_bus(m, "floppy-bus.0", "floppy-bus"); //FIXME: use macro
+    machine_class_add_always_available_bus(m, "i2c", "i2c-bus"); //FIXME: use macro
+    machine_class_add_always_available_bus(m, "pci.0", TYPE_PCI_BUS);
+    machine_class_add_always_available_bus(m, "isa.0", TYPE_ISA_BUS);
+    machine_class_add_always_available_bus(m, "ide.0", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.1", "IDE");//FIXME: use macro
 }
 
 DEFINE_PC_MACHINE(xenfv, "xenfv", pc_xen_hvm_init,
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index b40d19e..11f918c 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -283,6 +283,9 @@ static void pc_q35_init(MachineState *machine)
 
 static void pc_q35_machine_options(MachineClass *m)
 {
+    MachineBusInfo *pcie;
+    strList *new;
+
     m->family = "pc_q35";
     m->desc = "Standard PC (Q35 + ICH9, 2009)";
     m->hot_add_cpu = pc_hot_add_cpu;
@@ -292,6 +295,24 @@ static void pc_q35_machine_options(MachineClass *m)
     m->no_floppy = 1;
     m->has_dynamic_sysbus = true;
     m->max_cpus = 288;
+
+    pcie = machine_class_add_always_available_bus(m, "pcie.0", TYPE_PCIE_BUS);
+    /* The root bus doesn't use the TYPE_PCIE_BUS default: it also accepts
+     * legacy PCI devices.
+     */
+    new = g_new0(strList, 1);
+    new->value = g_strdup(INTERFACE_LEGACY_PCI_DEVICE);
+    new->next = pcie->accepted_device_types;
+    pcie->accepted_device_types = new;
+
+    machine_class_add_always_available_bus(m, "i2c", "i2c-bus"); //FIXME: use macro
+    machine_class_add_always_available_bus(m, "isa.0", TYPE_ISA_BUS);
+    machine_class_add_always_available_bus(m, "ide.0", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.1", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.2", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.3", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.4", "IDE");//FIXME: use macro
+    machine_class_add_always_available_bus(m, "ide.5", "IDE");//FIXME: use macro
 }
 
 static void pc_q35_2_8_machine_options(MachineClass *m)
