Index: uspace/lib/drv/generic/remote_usbdiag.c
===================================================================
--- uspace/lib/drv/generic/remote_usbdiag.c	(revision 7cba9f73d4bf1357e8b015cf70d85178e89a2c01)
+++ uspace/lib/drv/generic/remote_usbdiag.c	(revision 298e010a92da9d58342932870b1eeba77247be65)
@@ -58,5 +58,5 @@
 }
 
-int usbdiag_test_in(async_exch_t *exch, const usbdiag_test_params_t *params, usbdiag_test_results_t *results)
+errno_t usbdiag_test_in(async_exch_t *exch, const usbdiag_test_params_t *params, usbdiag_test_results_t *results)
 {
 	if (!exch)
@@ -66,5 +66,5 @@
 	aid_t req = async_send_1(exch, DEV_IFACE_ID(USBDIAG_DEV_IFACE), IPC_M_USBDIAG_TEST_IN, &answer);
 
-	int rc = async_data_write_start(exch, params, sizeof(usbdiag_test_params_t));
+	errno_t rc = async_data_write_start(exch, params, sizeof(usbdiag_test_params_t));
 	if (rc != EOK) {
 		async_exchange_end(exch);
@@ -85,8 +85,8 @@
 	async_wait_for(req, &retval);
 
-	return (int) retval;
-}
-
-int usbdiag_test_out(async_exch_t *exch, const usbdiag_test_params_t *params, usbdiag_test_results_t *results)
+	return (errno_t) retval;
+}
+
+errno_t usbdiag_test_out(async_exch_t *exch, const usbdiag_test_params_t *params, usbdiag_test_results_t *results)
 {
 	if (!exch)
@@ -96,5 +96,5 @@
 	aid_t req = async_send_1(exch, DEV_IFACE_ID(USBDIAG_DEV_IFACE), IPC_M_USBDIAG_TEST_OUT, &answer);
 
-	int rc = async_data_write_start(exch, params, sizeof(usbdiag_test_params_t));
+	errno_t rc = async_data_write_start(exch, params, sizeof(usbdiag_test_params_t));
 	if (rc != EOK) {
 		async_exchange_end(exch);
@@ -115,5 +115,5 @@
 	async_wait_for(req, &retval);
 
-	return (int) retval;
+	return (errno_t) retval;
 }
 
@@ -158,5 +158,5 @@
 
 	usbdiag_test_results_t results;
-	const int ret = !diag_iface->test_in ? ENOTSUP : diag_iface->test_in(fun, &params, &results);
+	const errno_t ret = !diag_iface->test_in ? ENOTSUP : diag_iface->test_in(fun, &params, &results);
 
 	if (ret != EOK) {
@@ -210,5 +210,5 @@
 
 	usbdiag_test_results_t results;
-	const int ret = !diag_iface->test_out ? ENOTSUP : diag_iface->test_out(fun, &params, &results);
+	const errno_t ret = !diag_iface->test_out ? ENOTSUP : diag_iface->test_out(fun, &params, &results);
 
 	if (ret != EOK) {
Index: uspace/lib/drv/include/usbdiag_iface.h
===================================================================
--- uspace/lib/drv/include/usbdiag_iface.h	(revision 7cba9f73d4bf1357e8b015cf70d85178e89a2c01)
+++ uspace/lib/drv/include/usbdiag_iface.h	(revision 298e010a92da9d58342932870b1eeba77247be65)
@@ -65,11 +65,11 @@
 void usbdiag_disconnect(async_sess_t*);
 
-int usbdiag_test_in(async_exch_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
-int usbdiag_test_out(async_exch_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
+errno_t usbdiag_test_in(async_exch_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
+errno_t usbdiag_test_out(async_exch_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
 
 /** USB diagnostic device communication interface. */
 typedef struct {
-	int (*test_in)(ddf_fun_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
-	int (*test_out)(ddf_fun_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
+	errno_t (*test_in)(ddf_fun_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
+	errno_t (*test_out)(ddf_fun_t*, const usbdiag_test_params_t *, usbdiag_test_results_t *);
 } usbdiag_iface_t;