diff --git a/src/functional/fdopen.c b/src/functional/fdopen.c
index 392a1b1..88f7561 100644
--- a/src/functional/fdopen.c
+++ b/src/functional/fdopen.c
@@ -1,6 +1,3 @@
-#ifndef _XOPEN_SOURCE
-#define _XOPEN_SOURCE 700
-#endif
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>