diff --git a/module/mes/posix.mes b/module/mes/posix.mes
index 85a85983..1eec487a 100644
--- a/module/mes/posix.mes
+++ b/module/mes/posix.mes
@@ -24,3 +24,10 @@
 
 (define R_OK 0)
 (define S_IRWXU #o700)
+
+(define (basename file-name . ext)
+  (let ((base (last (string-split file-name #\/)))
+        (ext (and (pair? ext) (car ext))))
+    (if (and ext
+             (string-suffix? ext base)) (string-drop-right base (string-length ext))
+             base)))