diff --git a/rootston/input.c b/rootston/input.c
index de847d78..b7a5f1ba 100644
--- a/rootston/input.c
+++ b/rootston/input.c
@@ -1,4 +1,4 @@
-#define _POSIX_C_SOURCE 199309L
+#define _POSIX_C_SOURCE 200112L
 #include <assert.h>
 #include <stdlib.h>
 #include <time.h>