Index: uspace/lib/usbvirt/callback.c
===================================================================
--- uspace/lib/usbvirt/callback.c	(revision 100962316f11f4d28cc4be7eaf39ac3705dc69ca)
+++ uspace/lib/usbvirt/callback.c	(revision ea5dbaf1f4de23f270945fc8c03b2eff47c7a95e)
@@ -155,5 +155,5 @@
 	 * If the request was processed, we will send data back.
 	 */
-	if (rc == EOK) {
+	if ((rc == EOK) && (expected_len > 0)) {
 		size_t receive_len;
 		ipc_callid_t callid;