The Tanglewood Festival has announced a cast change for the July 29 performance.

The festival said that “mezzo-soprano Isabel Leonard has had to withdraw from this Saturday’s performance of Berlioz’s ‘Les Nuits d’été’ due to illness.”

As a result, American contralto Avery Amereau will make her BSO debut and will perform the Berlioz in her place. The remainder of the program, under the direction of guest conductor Dima Slobodeniouk, is unchanged.

Amereau has performed at the Metropolitan Opera, Bayerische Staatsoper, Santa Fe Opera, Seattle Opera, Opéra de Lyon, Grand Théâtre de Genève, and English National Opera, along with the Glyndebourne and Salzburg festivals. In future seasons, she is set to make house debuts with the Royal Opera House, Covent Garden, and Royal Danish Opera.