Index: uspace/lib/usb/src/ddfiface.c
===================================================================
--- uspace/lib/usb/src/ddfiface.c	(revision 1e6dc5b53b33bd0abfbfab8a742f6a9f8c664cee)
+++ uspace/lib/usb/src/ddfiface.c	(revision 1c1b57723631eced3f412c2102d9f8b1aca38d0b)
@@ -96,4 +96,5 @@
 {
 	assert(fun);
+	assert(handle == 0);
 
 	async_sess_t *parent_sess =