diff --git a/src/session.c b/src/session.c
index 0a8db0e..8e6c312 100644
--- a/src/session.c
+++ b/src/session.c
@@ -3,7 +3,7 @@
  * \author Michal Vasko <mvasko@cesnet.cz>
  * \brief libnetconf2 - general session functions
  *
- * Copyright (c) 2015 - 2017 CESNET, z.s.p.o.
+ * Copyright (c) 2015 - 2018 CESNET, z.s.p.o.
  *
  * This source code is licensed under BSD 3-Clause License (the "License").
  * You may not use this file except in compliance with the License.
@@ -11,11 +11,13 @@
  *
  *     https://opensource.org/licenses/BSD-3-Clause
  */
+#define _DEFAULT_SOURCE
 
 #include <assert.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include <pthread.h>
 #include <sys/time.h>
 #include <time.h>