write JSON to file as lazy ByteString directly from Aeson encode output without converting to String

Question

Currently, I'm using something like this to write JSON content (my_json) to a file (my_output_filepath):

import           Data.Aeson.Encode.Pretty
import qualified Data.ByteString.Lazy.UTF8 as U

writeFile my_output_filepath $ U.toString $ encodePretty my_json

This works, but I'm wondering whether it is necessary to convert the ByteString that is returned by (encodePretty) to a String before writing it to a file, or if it incurs a performance penalty.

I see there is a variant of writeFile that accepts a ByteString as input. However, when I try to use it, I get this error:

Couldn't match expected type ‘B.ByteString’
            with actual type ‘U.ByteString’
NB: ‘B.ByteString’ is defined in ‘Data.ByteString.Internal’
    ‘U.ByteString’ is defined in ‘Data.ByteString.Lazy.Internal’

Is there some way to get the Lazy variant of ByteString to interoperate with writeFile?