diff --git a/mes/module/mes/posix.mes b/mes/module/mes/posix.mes
index fc1b1574..fa8c679c 100644
--- a/mes/module/mes/posix.mes
+++ b/mes/module/mes/posix.mes
@@ -1,7 +1,7 @@
 ;;; -*-scheme-*-
 
 ;;; GNU Mes --- Maxwell Equations of Software
-;;; Copyright © 2017 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+;;; Copyright © 2017, 2023 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;;
 ;;; This file is part of GNU Mes.
 ;;;
@@ -24,7 +24,7 @@
 
 (mes-use-module (srfi srfi-13))
 
-(define R_OK 0)
+(define R_OK 4)
 (define S_IRWXU #o700)
 
 (define (basename file-name . ext)