diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index b8131febb6d8..7492a4bbc08f 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -1199,6 +1199,25 @@ device_shutdown(device_t dev)
     return DEVICE_SHUTDOWN(dev);
 }
 
+int
+device_set_unit(device_t dev, int unit)
+{
+    devclass_t dc;
+    int err;
+
+    dc = device_get_devclass(dev);
+    if (unit < dc->maxunit && dc->devices[unit])
+	return EBUSY;
+    err = devclass_delete_device(dc, dev);
+    if (err)
+	return err;
+    dev->unit = unit;
+    err = devclass_add_device(dc, dev);
+    if (err)
+	return err;
+    return 0;
+}
+
 #ifdef DEVICE_SYSCTLS
 
 /*
diff --git a/sys/sys/bus.h b/sys/sys/bus.h
index 84176db97551..77bd9030d572 100644
--- a/sys/sys/bus.h
+++ b/sys/sys/bus.h
@@ -257,6 +257,7 @@ void	device_set_desc_copy(device_t dev, const char* desc);
 int	device_set_devclass(device_t dev, const char *classname);
 int	device_set_driver(device_t dev, driver_t *driver);
 void	device_set_flags(device_t dev, u_int32_t flags);
+int	device_set_unit(device_t dev, int unit);	/* XXX DONT USE XXX */
 int	device_shutdown(device_t dev);
 void	device_unbusy(device_t dev);
 void	device_verbose(device_t dev);