Custom route, but keep some routes as the automatic ones

Question

I've added a few Actions on top of the CRUD ones, and I want to have custom routes to the new actions. But still, keep the CRUD actions with the same route (e.g. /ShowPost?postId=[uuid]

instance HasPath PostsController where
    -- ...
    pathTo ShowPostAction { postId } = "/ShowPost?postId=" ++ tshow postId


instance CanRoute PostsController where
   parseRoute' = do
       let posts = do
           string "/Posts"
           optional "/"
           endOfInput
           pure PostsAction

       let showPost = do
           string "/ShowPost?postId="
           postId <- parseId
           optional "/"
           endOfInput
           pure ShowPostAction { postId }


       posts <|> showPosts -- ...

I assume the CanRoute part isn't parsing correctly, as I end up with a 404 page when navigating to /ShowPost?postId=...