What's wrong with my labels?

PS[19]> (ps (defun fac (n) (labels ((f (n a)
    (if (< n 2)
         a
         (f (- n 1) (* n a)))))
   (f n 1)))
)

*** - The object to be destructured should be a list with 0 elements, not
      ((- N 1) (* N A)).
The following restarts are available:
ABORT          :R1      Abort main loop
Break 1 PS[20]>