diff --git a/cftw.c b/cftw.c
index bb05843..c4986fd 100644
--- a/cftw.c
+++ b/cftw.c
@@ -1,3 +1,5 @@
+#define _POSIX_C_SOURCE 200809L
+
 #include "cftw.h"
 #include <dynstr.h>
 #include <dirent.h>