diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -542,7 +542,10 @@
 #define	_POSIX_C_SOURCE		198808
 #endif
 #ifdef _POSIX_C_SOURCE
-#if _POSIX_C_SOURCE >= 200809
+#if _POSIX_C_SOURCE >= 202405
+#define	__POSIX_VISIBLE		202405
+#define	__ISO_C_VISIBLE		2017
+#elif _POSIX_C_SOURCE >= 200809
 #define	__POSIX_VISIBLE		200809
 #define	__ISO_C_VISIBLE		1999
 #elif _POSIX_C_SOURCE >= 200112