SQLite warning automatic index on SubQuery

I have the following SQL

SELECT *
FROM Genres, GenreImages 
LEFT JOIN 
(SELECT SUM(Movies.PlayCount) AS SummedPlayCounts, MovieGenres.GenreId 
FROM Movies, MovieGenres 
WHERE Movies.Id = MovieGenres.MovieId 
GROUP BY MovieGenres.GenreId 
ORDER BY SummedPlayCounts DESC) AS GenreMoviesPlayCounts 
ON GenreMoviesPlayCounts.GenreId = Genre.Id 
WHERE GenreImages.GenreId = Genres.Id 
AND GenreImages.PrimaryImage = 1

it throws

SQLite warning (284): automatic index on sqlite_sq_BD26FF8(GenreId)

MovieGenres.GenreId does have an index, as does GenreImages.GenreId. This warning is coming from the subquery GenreMoviesPlayCounts.GenreId = Genre.Id.

Is there a better way to do this that makes use of my existing index or doesn't need a sub query?