diff --git a/otherlibs/bigarray/mmap_unix.c b/otherlibs/bigarray/mmap_unix.c
index 69a83361b..1dfc4237c 100644
--- a/otherlibs/bigarray/mmap_unix.c
+++ b/otherlibs/bigarray/mmap_unix.c
@@ -15,7 +15,7 @@
 
 /* Needed (under Linux at least) to get pwrite's prototype in unistd.h.
    Must be defined before the first system .h is included. */
-#define _XOPEN_SOURCE 500
+#define _XOPEN_SOURCE 600
 
 #include <stddef.h>
 #include <string.h>