diff --git a/src/lua/fio.cc b/src/lua/fio.cc
index bb1453247a944c2f62115b2e21ad83c6a66c628d..911c29a4971761517cdfb1e98070a9e5822bd111 100644
--- a/src/lua/fio.cc
+++ b/src/lua/fio.cc
@@ -26,6 +26,7 @@
  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+#define _POSIX_SOURCE
 #include "lua/fio.h"
 #include <sys/types.h>
 #include <sys/stat.h>