diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 82a7daa188385b9275bc61160cfa4eb274edf18b..d045e8b4547e1da3c79d7275491103a22789d52a 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1524,6 +1524,7 @@ static void pc_generic_machine_class_init(ObjectClass *oc, void *data)
     mc->hot_add_cpu = qm->hot_add_cpu;
     mc->kvm_type = qm->kvm_type;
     mc->block_default_type = qm->block_default_type;
+    mc->units_per_default_bus = qm->units_per_default_bus;
     mc->max_cpus = qm->max_cpus;
     mc->no_serial = qm->no_serial;
     mc->no_parallel = qm->no_parallel;
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index d4a907c71b7fa748d3c42516a605a1118a09bcda..b28ddbb74239bb913e276013dc74fb44c8e50067 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -344,7 +344,8 @@ static void pc_q35_init_1_4(MachineState *machine)
 #define PC_Q35_MACHINE_OPTIONS \
     PC_DEFAULT_MACHINE_OPTIONS, \
     .desc = "Standard PC (Q35 + ICH9, 2009)", \
-    .hot_add_cpu = pc_hot_add_cpu
+    .hot_add_cpu = pc_hot_add_cpu, \
+    .units_per_default_bus = 1
 
 #define PC_Q35_2_2_MACHINE_OPTIONS                      \
     PC_Q35_MACHINE_OPTIONS,                             \
diff --git a/include/hw/boards.h b/include/hw/boards.h
index dfb6718dc184c8c3eb0fe2392703a386f8efe767..663f16acdd2e655f636c5c9c1960f8e72ca501f2 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -28,6 +28,7 @@ struct QEMUMachine {
     QEMUMachineHotAddCPUFunc *hot_add_cpu;
     QEMUMachineGetKvmtypeFunc *kvm_type;
     BlockInterfaceType block_default_type;
+    int units_per_default_bus;
     int max_cpus;
     unsigned int no_serial:1,
         no_parallel:1,
@@ -86,6 +87,7 @@ struct MachineClass {
     int (*kvm_type)(const char *arg);
 
     BlockInterfaceType block_default_type;
+    int units_per_default_bus;
     int max_cpus;
     unsigned int no_serial:1,
         no_parallel:1,
diff --git a/vl.c b/vl.c
index 4bc8f97c25a2e300bf856fec177e69fbcc51125b..debcbcceea8957dd342ec00d08768dc1925bae85 100644
--- a/vl.c
+++ b/vl.c
@@ -1585,6 +1585,7 @@ static void machine_class_init(ObjectClass *oc, void *data)
     mc->hot_add_cpu = qm->hot_add_cpu;
     mc->kvm_type = qm->kvm_type;
     mc->block_default_type = qm->block_default_type;
+    mc->units_per_default_bus = qm->units_per_default_bus;
     mc->max_cpus = qm->max_cpus;
     mc->no_serial = qm->no_serial;
     mc->no_parallel = qm->no_parallel;
@@ -4375,6 +4376,13 @@ int main(int argc, char **argv, char **envp)
     blk_mig_init();
     ram_mig_init();
 
+    /* If the currently selected machine wishes to override the units-per-bus
+     * property of its default HBA interface type, do so now. */
+    if (machine_class->units_per_default_bus) {
+        override_max_devs(machine_class->block_default_type,
+                          machine_class->units_per_default_bus);
+    }
+
     /* open the virtual block devices */
     if (snapshot)
         qemu_opts_foreach(qemu_find_opts("drive"), drive_enable_snapshot, NULL, 0);