StandaloneDeriving and DeriveAnyClass don't work together

I'm starting with the SPretty example from the DeriveAnyClass section in the GHC users guide:

#!/usr/bin/env stack
-- stack --resolver lts-8.0
{-# LANGUAGE DefaultSignatures, DeriveAnyClass, StandaloneDeriving #-}

import Prelude
import Numeric.Natural (Natural)

class SPretty a where
    sPpr :: a -> String
    default sPpr :: Show a => a -> String
    sPpr = show

I can write an empty instance for Natural:

instance SPretty Natural where

So then I would expect to be able to write an equivalent definition using StandaloneDeriving and DeriveAnyClass:

deriving instance SPretty Natural

But instead it fails with this error:

error:
    • Can't make a derived instance of ‘SPretty Natural’:
        The data constructors of ‘Natural’ are not all in scope
          so you cannot derive an instance for it
    • In the stand-alone deriving instance for ‘SPretty Natural’

It seems like this ought to work; I'm not sure why the constructors should need to be in scope, given that the instance can be derived trivially without defining any methods.