Index: head/sys/dev/pci/pci_iov.c
===================================================================
--- head/sys/dev/pci/pci_iov.c
+++ head/sys/dev/pci/pci_iov.c
@@ -586,7 +586,7 @@
 		 * VFs.
 		 */
 		if (nvlist_get_bool(iov_config, "passthrough"))
-			device_set_devclass(vf, "ppt");
+			device_set_devclass_fixed(vf, "ppt");
 
 		vfinfo = device_get_ivars(vf);
 
Index: head/sys/kern/subr_bus.c
===================================================================
--- head/sys/kern/subr_bus.c
+++ head/sys/kern/subr_bus.c
@@ -2683,6 +2683,25 @@
 }
 
 /**
+ * @brief Set the devclass of a device and mark the devclass fixed.
+ * @see device_set_devclass()
+ */
+int
+device_set_devclass_fixed(device_t dev, const char *classname)
+{
+	int error;
+
+	if (classname == NULL)
+		return (EINVAL);
+
+	error = device_set_devclass(dev, classname);
+	if (error)
+		return (error);
+	dev->flags |= DF_FIXEDCLASS;
+	return (0);
+}
+
+/**
  * @brief Set the driver of a device
  *
  * @retval 0		success
Index: head/sys/sys/bus.h
===================================================================
--- head/sys/sys/bus.h
+++ head/sys/sys/bus.h
@@ -522,6 +522,7 @@
 void	device_set_desc(device_t dev, const char* desc);
 void	device_set_desc_copy(device_t dev, const char* desc);
 int	device_set_devclass(device_t dev, const char *classname);
+int	device_set_devclass_fixed(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);
 void	device_set_softc(device_t dev, void *softc);