diff --git a/contrib/20.for/piclib/for.scm b/contrib/20.for/piclib/for.scm
index bd421ef8..d37afd9f 100644
--- a/contrib/20.for/piclib/for.scm
+++ b/contrib/20.for/piclib/for.scm
@@ -15,4 +15,7 @@
   (define (yield x)
     (list x))
 
-  (export for in yield))
+  (define (null . x)
+    '())
+
+  (export for in yield null))