By Mike Bruno
Updated May 06, 2009 at 01:12 PM EDT

Kaitlin Olson, who plays Sweet Dee on the FX comedy It’s Always Sunny in Philadelphia, has been cast in the romantic comedy Leap Year, according to The Hollywood Reporter. She joins Amy Adams, Bill Nighy, Matthew Goode, and Adam Scott in the movie, which is about 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 — a proposal he is traditionally bound to accept. Olson plays the married older sister of Adams’ character.