Index: uspace/drv/bus/usb/uhci/hc.c
===================================================================
--- uspace/drv/bus/usb/uhci/hc.c	(revision 34d750c26e597cd2948893deb14ffb915ac33278)
+++ uspace/drv/bus/usb/uhci/hc.c	(revision 3ac86a42de2e8948db2e3047654b63338c68e55f)
@@ -344,5 +344,11 @@
 
 	transfer_list_t *list = hc->transfers[ep->device->speed][ep->transfer_type];
-	assert(list);
+
+	if (!list)
+		/*
+		 * We don't support this combination (e.g. isochronous),
+		 * so no transfer can be active.
+		 */
+		return;
 
 	// To avoid ABBA deadlock, we need to take the list first