diff --git a/hw/core/machine.c b/hw/core/machine.c
index cb1185a..25c45e6 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -223,6 +223,7 @@
     MachineState *ms = MACHINE(obj);
 
     ms->usb = value;
+    ms->usb_disabled = !value;
 }
 
 static char *machine_get_firmware(Object *obj, Error **errp)
diff --git a/hw/ppc/mac_newworld.c b/hw/ppc/mac_newworld.c
index 624b4ab..7cc5106 100644
--- a/hw/ppc/mac_newworld.c
+++ b/hw/ppc/mac_newworld.c
@@ -371,7 +371,7 @@
         /* 970 gets a U3 bus */
         pci_bus = pci_pmac_u3_init(pic, get_system_memory(), get_system_io());
         machine_arch = ARCH_MAC99_U3;
-        machine->usb |= defaults_enabled();
+        machine->usb |= defaults_enabled() && !machine->usb_disabled;
     } else {
         pci_bus = pci_pmac_init(pic, get_system_memory(), get_system_io());
         machine_arch = ARCH_MAC99;
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index ca0a060..61ddc79 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1580,7 +1580,7 @@
     /* Graphics */
     if (spapr_vga_init(phb->bus)) {
         spapr->has_graphics = true;
-        machine->usb |= defaults_enabled();
+        machine->usb |= defaults_enabled() && !machine->usb_disabled;
     }
 
     if (machine->usb) {
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 78838d1..1f11881 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -146,6 +146,7 @@
     bool dump_guest_core;
     bool mem_merge;
     bool usb;
+    bool usb_disabled;
     char *firmware;
     bool iommu;
     bool suppress_vmdesc;