diff --git a/client/sub_client_output.c b/client/sub_client_output.c
index 784299cd..90b5b58a 100644
--- a/client/sub_client_output.c
+++ b/client/sub_client_output.c
@@ -14,7 +14,7 @@ Contributors:
    Roger Light - initial implementation and documentation.
 */
 
-#define _POSIX_C_SOURCE 199309L
+#define _POSIX_C_SOURCE 200809L
 
 #include <assert.h>
 #include <errno.h>