Frank, who plans to retire from Congress this year after 16 terms, became the first openly gay member of Congress in 1987. Frank announced in January his plan to marry longtime partner Jim Ready. The marriage will take place in Massachusetts, one of the six states that have legalized gay marriage.

“I do think, to be honest, if I was running for reelection, I might have tried to put the marriage off until after the election, because it just becomes a complication,” Frank said in the interview. “But I did want to get married while I was still in office.” He called the ability to do so before he retires an “unintended benefit.”

Frank, who has staunchly supported LGBT rights as a legislator both before and after voluntarily coming out, said he has been “pleasantly surprised” at how “quickly” the gay-rights movement has progressed in the last 40 years. Asked what he defines as his most significant accomplishment in office, Frank said he takes “very substantial credit” in last year’s repeal of the military’s official policy against openly gay service members, known as “Don’t ask, don’t tell.”

He went on to predict that “within 10 years, we’re going to have pretty close to full legal equality for gay and lesbian people in much of America.”