The actor and late-night host were tasked on Thursday with guessing which popular song The Roots were playing. The Roots put a unique twist on every song by performing it in the wrong key, wrong tempo or wrong genre.
Fallon was up first and quickly guessed "Party in the U.S.A." by Miley Cyrus, which was given more of a reggae sound.
McConaughey had a harder time deciphering a jazz version of "Joy to the World" by Three Dog Night.
The pair ended the game by seeing who could guess the next song first. Fallon won, after realizing that The Roots were playing a softer version of "I Love Rock 'N Roll" by Joan Jett.
McConaughey is set to release a memoir titled Greenlights on Oct. 20. The actor has said the book is based on journals he kept for years.
"I'd call it an aspirational book. It's about an approach to life. It's stories, insights, philosophies that you and anyone else can objectively understand," the 50-year-old told Fallon about the memoir.