diff --git a/lisp/emacs-lisp/byte-run.el b/lisp/emacs-lisp/byte-run.el
index 0bb0495..d671892 100644
--- a/lisp/emacs-lisp/byte-run.el
+++ b/lisp/emacs-lisp/byte-run.el
@@ -180,6 +180,10 @@ The return value is undefined.
   ;; from
   ;;    (defun foo (arg) (toto)).
   (declare (doc-string 3))
+  (if (null
+       (and (listp arglist)
+            (null (delq t (mapcar #'symbolp arglist)))))
+      (error "Malformed arglist: %s" arglist))
   (let ((decls (cond
                 ((eq (car-safe docstring) 'declare)
                  (prog1 (cdr docstring) (setq docstring nil)))
@@ -209,7 +213,7 @@ The return value is undefined.
                     nil)
                    (t (message "Warning: Unknown defun property `%S' in %S"
                                (car x) name)))))
-                   decls))
+            decls))
           (def (list 'defalias
                      (list 'quote name)
                      (list 'function
-- 
1.8.1.5