diff --git a/ansi-tests/ansi-aux.lsp b/ansi-tests/ansi-aux.lsp
index e24df14cfc9a8f1b5f5bbe80f03abd73781d0157..f860418e4ef52f69b9d1d8390e7c3e9fb1be98cb 100644
--- a/ansi-tests/ansi-aux.lsp
+++ b/ansi-tests/ansi-aux.lsp
@@ -37,7 +37,7 @@
   (etypecase fn
     (function fn)
     (symbol (symbol-function fn))
-    ((cons (eql setf) symbol) (fdefinition fn))))    
+    ((cons (eql setf) (cons symbol nil)) (fdefinition fn))))
 
 ;;; Macro to check that a function is returning a specified number of values
 ;;; (defaults to 1)