diff --git a/libserialport_internal.h b/libserialport_internal.h
index 962fc20..bef84b6 100644
--- a/libserialport_internal.h
+++ b/libserialport_internal.h
@@ -18,6 +18,11 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifdef __linux__
+#define _BSD_SOURCE // for timeradd, timersub, timercmp
+#define _XOPEN_SOURCE 700 // for readlinkat
+#endif
+
 #include <string.h>
 #include <sys/types.h>
 #include <sys/stat.h>