diff --git a/scheme/opt/flatten.scm b/scheme/opt/flatten.scm
index 40a8717..3196a6b 100644
--- a/scheme/opt/flatten.scm
+++ b/scheme/opt/flatten.scm
@@ -9,7 +9,7 @@
 (set-optimizer! 'flat-environments
   (lambda (forms package)
     (map (lambda (form)
-	   (flatten-form (force form)))
+	   (flatten-form (force-node form)))
 	 forms)))
 
 (define (flatten-form node)