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The musician and actor recently posted the selfie on his Instagram, in which he was seen in a voting booth in his native Tennessee. (The photo was later removed from Instagram.)
Appearing on Jimmy Fallon's "Tonight Show" Wednesday night, Timberlake told the audience that they should "get out and vote," but maybe not follow his other step.
"Don't take a picture of yourself," Timberlake said. "I had no idea."
Tennessee is one of a number of states in which recording a photo or video in a polling place is illegal. You can see the full list at ABC News.
Watch Justin Timberlake on the "Tonight Show" below: