diff --git a/include/dalist/dalist_env.h b/include/dalist/dalist_env.h
index 2f2b57a..8c8ab0f 100644
--- a/include/dalist/dalist_env.h
+++ b/include/dalist/dalist_env.h
@@ -7,6 +7,10 @@
 
 #else
 
+#ifndef _XOPEN_SOURCE
+#define _XOPEN_SOURCE 500
+#endif
+
 #include <stdint.h>
 #include <stdio.h>
 #include <errno.h>