diff --git a/asdf-bundle.lisp b/asdf-bundle.lisp
index b547beb7f63330fce88020e42ca64c051d44cc2c..9918d9677b5f4f8826fc5781881668761d5d36bf 100644
--- a/asdf-bundle.lisp
+++ b/asdf-bundle.lisp
@@ -427,7 +427,6 @@ using WRITE-SEQUENCE and a sensibly sized buffer." ; copied from xcvb-driver
   (make-pathname :name (strcat (pathname-name pathname) suffix)
                  :defaults pathname))
 
-#+(or allegro clisp clozure cmu lispworks sbcl scl)
 (defun combine-fasls (inputs output)
   #+clozure (ccl:fasl-concatenate output inputs :if-exists :supersede)
   #+(or allegro clisp cmu sbcl scl) (concatenate-files inputs output)
@@ -449,7 +448,9 @@ using WRITE-SEQUENCE and a sensibly sized buffer." ; copied from xcvb-driver
                            :collect `(,(namestring f) :load-only t))))
            (scm:concatenate-system output :fasls-to-concatenate))
       (loop :for f :in fasls :do (ignore-errors (delete-file f)))
-      (ignore-errors (lispworks:delete-system :fasls-to-concatenate)))))
+      (ignore-errors (lispworks:delete-system :fasls-to-concatenate))))
+  #-(or allegro clisp clozure cmu lispworks sbcl scl)
+  (error "~S is not supported on ~A" 'combine-fasls (implementation-type)))
 
 (defun call-with-staging-pathname (pathname fun)
   "Calls fun with a staging pathname, and atomically