--- ./seccompsandbox.c.orig
+++ ./seccompsandbox.c
@@ -12,6 +12,9 @@
 
 #if defined(__linux__) && defined(__x86_64__)
 
+/* for O_DIRECTORY */
+#define _GNU_SOURCE
+
 #include "session.h"
 #include "sysutil.h"
 #include "tunables.h"