diff --git a/endlessh.c b/endlessh.c
index 0676e92..90543aa 100644
--- a/endlessh.c
+++ b/endlessh.c
@@ -1,4 +1,4 @@
-#define _POSIX_C_SOURCE 200112L
+#define _XOPEN_SOURCE 600
 #include <time.h>
 #include <errno.h>
 #include <stdio.h>