Avril and Katy Rock as 'Idol' Judges

Avril Lavigne and Katy Perry will serve as guest judges on American Idol

The cast of characters taking the open judge's musical chair on "American Idol" continues to grow. EW.com reports pop punktress Avril Lavigne and sexy singer Katy Perry will serve as guest judges on "Idol."

Sources tell EW.com that Lavigne and Perry will each spend one day as a judge when "Idol" films the callback auditions in Los Angeles.

Perry was rumored to have subbed at an "Idol" audition a few weeks back, but the "Waking Up in Vegas" songstress was never scheduled.

Victoria Beckham, Mary J. Blige, Neil Patrick Harris, Shania Twain, Kristin Chenoweth and Joe Jonas have also filled Paula Abdul's seat at the "Idol" judges' table.

'American Idol' Guest Judges

Posh Judge

Victoria Beckham joined the judges during the Denver and Boston auditions.

No More Drama

Mary J. Blige served as a judge for the Atlanta auditions.

How I Met Your 'Idol'

Neil Patrick Harris judged the Dallas auditions.

Country Crooner

Shania Twain judgedin Chicago.

'Daisy' Judge

Kristin Chenoweth joined the panel for the Orlando auditions.

'Burnin' Up' for 'Idol'

Joe Jonas judged the Dallas auditions.

'Complicated' Judging Panel

Avril Lavigne will join the judges in Los Angeles.

'Waking Up' in L.A.

Katy Perry will decide what she likes at the Los Angeles auditions.