diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 3405583..eab6096 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -1163,7 +1163,7 @@
     for (i = 0; i < s->ports; i++) {
         AHCIDevice *ad = &s->dev[i];
 
-        ide_bus_new(&ad->port, qdev, i);
+        ide_bus_new(&ad->port, qdev, i, 1);
         ide_init2(&ad->port, irqs[i]);
 
         ad->hba = s;
diff --git a/hw/ide/cmd646.c b/hw/ide/cmd646.c
index 541d4ef..a73eb9a 100644
--- a/hw/ide/cmd646.c
+++ b/hw/ide/cmd646.c
@@ -281,7 +281,7 @@
 
     irq = qemu_allocate_irqs(cmd646_set_irq, d, 2);
     for (i = 0; i < 2; i++) {
-        ide_bus_new(&d->bus[i], &d->dev.qdev, i);
+        ide_bus_new(&d->bus[i], &d->dev.qdev, i, 2);
         ide_init2(&d->bus[i], irq[i]);
 
         bmdma_init(&d->bus[i], &d->bmdma[i], d);
diff --git a/hw/ide/internal.h b/hw/ide/internal.h
index 0efb2da..03f1489 100644
--- a/hw/ide/internal.h
+++ b/hw/ide/internal.h
@@ -450,6 +450,7 @@
     IDEDevice *slave;
     IDEState ifs[2];
     int bus_id;
+    int max_units;
     IDEDMA *dma;
     uint8_t unit;
     uint8_t cmd;
@@ -574,7 +575,7 @@
 void ide_atapi_cmd_reply_end(IDEState *s);
 
 /* hw/ide/qdev.c */
-void ide_bus_new(IDEBus *idebus, DeviceState *dev, int bus_id);
+void ide_bus_new(IDEBus *idebus, DeviceState *dev, int bus_id, int max_units);
 IDEDevice *ide_create_drive(IDEBus *bus, int unit, DriveInfo *drive);
 
 #endif /* HW_IDE_INTERNAL_H */
diff --git a/hw/ide/isa.c b/hw/ide/isa.c
index 5e7422f..369a7fa 100644
--- a/hw/ide/isa.c
+++ b/hw/ide/isa.c
@@ -69,7 +69,7 @@
 {
     ISAIDEState *s = ISA_IDE(dev);
 
-    ide_bus_new(&s->bus, DEVICE(dev), 0);
+    ide_bus_new(&s->bus, DEVICE(dev), 0, 2);
     ide_init_ioport(&s->bus, dev, s->iobase, s->iobase2);
     isa_init_irq(dev, &s->irq, s->isairq);
     ide_init2(&s->bus, s->irq);
diff --git a/hw/ide/macio.c b/hw/ide/macio.c
index 64b2406..bf12a10 100644
--- a/hw/ide/macio.c
+++ b/hw/ide/macio.c
@@ -334,7 +334,7 @@
     SysBusDevice *d = SYS_BUS_DEVICE(obj);
     MACIOIDEState *s = MACIO_IDE(obj);
 
-    ide_bus_new(&s->bus, DEVICE(obj), 0);
+    ide_bus_new(&s->bus, DEVICE(obj), 0, 2);
     memory_region_init_io(&s->mem, &pmac_ide_ops, s, "pmac-ide", 0x1000);
     sysbus_init_mmio(d, &s->mem);
     sysbus_init_irq(d, &s->irq);
diff --git a/hw/ide/mmio.c b/hw/ide/mmio.c
index ce88c3a..e80e7e5 100644
--- a/hw/ide/mmio.c
+++ b/hw/ide/mmio.c
@@ -137,7 +137,7 @@
     SysBusDevice *d = SYS_BUS_DEVICE(obj);
     MMIOState *s = MMIO_IDE(obj);
 
-    ide_bus_new(&s->bus, DEVICE(obj), 0);
+    ide_bus_new(&s->bus, DEVICE(obj), 0, 2);
     sysbus_init_irq(d, &s->irq);
 }
 
diff --git a/hw/ide/piix.c b/hw/ide/piix.c
index 1de284d..bf2856f 100644
--- a/hw/ide/piix.c
+++ b/hw/ide/piix.c
@@ -135,7 +135,7 @@
     int i;
 
     for (i = 0; i < 2; i++) {
-        ide_bus_new(&d->bus[i], &d->dev.qdev, i);
+        ide_bus_new(&d->bus[i], &d->dev.qdev, i, 2);
         ide_init_ioport(&d->bus[i], NULL, port_info[i].iobase,
                         port_info[i].iobase2);
         ide_init2(&d->bus[i], isa_get_irq(NULL, port_info[i].isairq));
diff --git a/hw/ide/qdev.c b/hw/ide/qdev.c
index 8a9a891..6a272b0 100644
--- a/hw/ide/qdev.c
+++ b/hw/ide/qdev.c
@@ -47,10 +47,11 @@
     .class_init = ide_bus_class_init,
 };
 
-void ide_bus_new(IDEBus *idebus, DeviceState *dev, int bus_id)
+void ide_bus_new(IDEBus *idebus, DeviceState *dev, int bus_id, int max_units)
 {
     qbus_create_inplace(&idebus->qbus, TYPE_IDE_BUS, dev, NULL);
     idebus->bus_id = bus_id;
+    idebus->max_units = max_units;
 }
 
 static char *idebus_get_fw_dev_path(DeviceState *dev)
@@ -76,6 +77,13 @@
     if (dev->unit == -1) {
         dev->unit = bus->master ? 1 : 0;
     }
+
+    if (dev->unit >= bus->max_units) {
+        error_report("Can't create IDE unit %d, bus supports only %d units",
+                     dev->unit, bus->max_units);
+        goto err;
+    }
+
     switch (dev->unit) {
     case 0:
         if (bus->master) {
diff --git a/hw/ide/via.c b/hw/ide/via.c
index 9d6a644..5fe053c 100644
--- a/hw/ide/via.c
+++ b/hw/ide/via.c
@@ -158,7 +158,7 @@
     int i;
 
     for (i = 0; i < 2; i++) {
-        ide_bus_new(&d->bus[i], &d->dev.qdev, i);
+        ide_bus_new(&d->bus[i], &d->dev.qdev, i, 2);
         ide_init_ioport(&d->bus[i], NULL, port_info[i].iobase,
                         port_info[i].iobase2);
         ide_init2(&d->bus[i], isa_get_irq(NULL, port_info[i].isairq));