diff --git a/src/io_backend/io_backend.c b/src/io_backend/io_backend.c
index 97fe974..0fd983e 100644
--- a/src/io_backend/io_backend.c
+++ b/src/io_backend/io_backend.c
@@ -1,3 +1,5 @@
+#define _POSIX_C_SOURCE 200809L
+
 #include "io_backend.h"
 
 #include <stdio.h>