diff --git a/src/wl_init.c b/src/wl_init.c
index 49e7cc52..3d48702b 100644
--- a/src/wl_init.c
+++ b/src/wl_init.c
@@ -26,6 +26,8 @@
 // It is fine to use C99 in this file because it will not be built with VS
 //========================================================================
 
+#define _POSIX_C_SOURCE 200809L
+
 #include "internal.h"
 
 #include <assert.h>