--- a/sys/bus/u4b/usb_hub.c
+++ b/sys/bus/u4b/usb_hub.c
@@ -1673,6 +1673,12 @@
 
 	sc = device_get_softc(parent);
 	hub = sc->sc_udev->hub;
+	if (hub == NULL) {
+		/* racing uhub_detach(): the hub is gone */
+		if (buflen)
+			buf[0] = 0;
+		return (0);
+	}
 
 	uhub_find_iface_index(hub, child, &res);
 	if (!res.udev) {
@@ -1716,6 +1722,12 @@
 
 	sc = device_get_softc(parent);
 	hub = sc->sc_udev->hub;
+	if (hub == NULL) {
+		/* racing uhub_detach(): the hub is gone */
+		if (buflen)
+			buf[0] = 0;
+		return (0);
+	}
 
 	uhub_find_iface_index(hub, child, &res);
 	if (!res.udev) {