diff --git a/sys/dev/usb/usb_subr.c b/sys/dev/usb/usb_subr.c
index d07ae9cfc990..7401b9dbfd37 100644
--- a/sys/dev/usb/usb_subr.c
+++ b/sys/dev/usb/usb_subr.c
@@ -895,6 +895,8 @@ usbd_set_config_index(struct usbd_device *dev, int index, int msg)
 		goto bad;
 	}
 
+	KASSERTMSG(dev->ud_ifaces == NULL, "ud_ifaces=%p", dev->ud_ifaces);
+
 	/* Allocate and fill interface data. */
 	nifc = cdp->bNumInterface;
 	if (nifc == 0) {