diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index b8679a71..acf6736a 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -500,7 +500,7 @@ netconn_accept(struct netconn *conn, struct netconn **new_conn)
 
   NETCONN_MBOX_WAITING_INC(conn);
   if (netconn_is_nonblocking(conn)) {
-    if (sys_arch_mbox_tryfetch(&conn->acceptmbox, &accept_ptr) == SYS_ARCH_TIMEOUT) {
+    if (sys_arch_mbox_tryfetch(&conn->acceptmbox, &accept_ptr) == SYS_MBOX_EMPTY) {
       API_MSG_VAR_FREE_ACCEPT(msg);
       NETCONN_MBOX_WAITING_DEC(conn);
       return ERR_WOULDBLOCK;
@@ -597,7 +597,7 @@ netconn_recv_data(struct netconn *conn, void **new_buf, u8_t apiflags)
   NETCONN_MBOX_WAITING_INC(conn);
   if (netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK) ||
       (conn->flags & NETCONN_FLAG_MBOXCLOSED) || (conn->pending_err != ERR_OK)) {
-    if (sys_arch_mbox_tryfetch(&conn->recvmbox, &buf) == SYS_ARCH_TIMEOUT) {
+    if (sys_arch_mbox_tryfetch(&conn->recvmbox, &buf) == SYS_MBOX_EMPTY) {
       err_t err;
       NETCONN_MBOX_WAITING_DEC(conn);
       err = netconn_err(conn);
diff --git a/src/api/tcpip.c b/src/api/tcpip.c
index 743553a5..a7e312a2 100644
--- a/src/api/tcpip.c
+++ b/src/api/tcpip.c
@@ -217,7 +217,7 @@ tcpip_thread_poll_one(void)
   int ret = 0;
   struct tcpip_msg *msg;
 
-  if (sys_arch_mbox_tryfetch(&tcpip_mbox, (void **)&msg) != SYS_ARCH_TIMEOUT) {
+  if (sys_arch_mbox_tryfetch(&tcpip_mbox, (void **)&msg) != SYS_MBOX_EMPTY) {
     LOCK_TCPIP_CORE();
     if (msg != NULL) {
       tcpip_thread_handle_msg(msg);