diff --git a/util/log.c b/util/log.c
index ae84f7e75..9996ab8ad 100644
--- a/util/log.c
+++ b/util/log.c
@@ -1,4 +1,4 @@
-#define _XOPEN_SOURCE 700 // for snprintf
+#define _POSIX_C_SOURCE 200809L
 #include <errno.h>
 #include <stdarg.h>
 #include <stdio.h>