diff --git a/compiler/knownfun.lisp b/compiler/knownfun.lisp
index 8399e32bef7a92f396a812414fecf099a02df793..3467aff7ef9801f7e78d858549e2a1678e72df0f 100644
--- a/compiler/knownfun.lisp
+++ b/compiler/knownfun.lisp
@@ -73,7 +73,7 @@
 	    (:print-function %print-function-info))
   ;;
   ;; Boolean attributes of this function.
-  (attributes nil :type attributes)
+  (attributes (required-argument) :type attributes)
   ;;
   ;; The transforms for this function.  An alist of (Function-Type . Function),
   ;; where Function-Type is the type that the call must have for Function to be