Comedian Jay Leno on Tuesday told Rick Santorum that he's wrong on gay marriage.

On NBC's The Tonight Show, Santorum gave Leno one of his signature sweater vests before Leno asked him his thoughts on gay marriage.

“I know you oppose gay marriage,” Leno told Santorum. “You're not going to change your mind on that, even though I think you're wrong, but that's okay.”

“Well, I think Barack Obama and Mitt Romney, think most of the people in political life, oppose gay marriage. At least they say they do,” the former GOP presidential nominee said.

“They just say they do. I think you really do,” Leno answered.

When asked about civil unions, Santorum returned to marriage.

“I think that marriage is an institution that has a defined benefit for society. Moms and dads coming together for the benefit of themselves and having children, for the benefit of continuing society going forward is something that government recognizes as a special union that's different than other relationships – not to say other relationships aren't important, that other relationships aren't valued and should be valued. But this is unique. It provides a unique benefit to society.”

Giving the example of gay couples raising adoptive children, Leno said gay marriage also benefits society. Santorum reiterated that he's also opposed to gay couples adopting children. (Watch the entire segment at