Kaitlin Olson cast in 'Leap Year'

Romantic comedy's stars include Amy Adams, Bill Nighy

Kaitlin Olson has joined the cast of Spyglass Entertainment's "Leap Year."

Amy Adams, Bill Nighy, Matthew Goode and Adam Scott also star in the romantic comedy about an American woman (Adams) who goes in search of her boyfriend in Ireland so she can propose to him on Leap Day, Feb. 29 -- which, according to tradition, requires him to say yes. Olson will play Libby, the married older sister of Adams' character, Anna.

Anand Tucker ("Shop Girl") is directing a screenplay by Harry Elfont and Deborah Kaplan ("Made of Honor"). Benderspink is producing.

Olson, repped by WMA and Flutie Entertainment, next returns for the fifth season of FX's "It's Always Sunny in Philadelphia." She has also appeared on "The Riches" and "Curb Your Enthusiasm."