(upgraded-array-element-type '(unsigned-byte 40))
FIXNUM
(defun foo (a) (declare (type (simple-array (unsigned-byte 40) (*)) a)) (aref a 0))
FOO
(foo (make-array 3 :element-type '(unsigned-byte 40) :initial-element 0))
> Error: The value #<VECTOR 3 type FIXNUM, simple> is not of the expected type CCL::SIMPLE-UNSIGNED-DOUBLEWORD-VECTOR.