ftype declaration

The following function declaration produces the following error when 
compiled at (float 0). At (float 1) it succeeds--and at (float 0) with no 
arguments it succeeds.

(declaim (optimize (float 0)))

(declaim (ftype (function (double-float) (values symbol double-float)) 
test))
(defun test (val)
  (values :valid val))

**++++ Error in TEST: 
  RESULT-TYPE (VALUES * DOUBLE-FLOAT) not one of (SINGLE-FLOAT 
DOUBLE-FLOAT T)
; (TOP-LEVEL-FORM 3)
; *** 1 error detected, no fasl file produced.
;;; Compilation finished with 0 warnings, 1 error.