ET caught up with the 38-year-old actor at the premiere of Girls' final season in New York City on Thursday, where he opened up about the body shaming Dunham has experienced throughout the course of the show.
"I was most frustrated by the physical criticism of some of our cast, specifically Lena. That was sort of baffling to me," Rannells shared. "I found myself getting very defensive on her behalf about it."
"Lena was able to sort of keep it in perspective, and really sort of let it go," he added of his co-star's ability to handle criticism. "[It] was a good lesson."
"She really does have this sort of innate sense of what people are thinking about, and what is going to be culturally relevant," Rannells said of "brilliant" Dunham. "She's always just a tick ahead of the curve, which is great."
After six seasons of proudly flaunting her naked body on Girls, Dunham agreed that she's learned not to take criticism personally.
"I think it was at first surprising to people to see a woman who looked or acted like someone they knew, who didn't have the sort of sheen or perfection of a television character," she told ET on the red carpet. "For some people that was refreshing, for some people it didn't constitute what they wanted to see on TV."
"I actually weirdly have a lot of friends that are models who were all like actually would say to me, 'I'm inspired by the way that you own your own body in this context,'" the 30-year-old actress continued. "My criticism wasn't from super fit people…It was from people who had been indoctrinated with a sense of their own body wasn't worth looking at. I actually have a lot of friends who are models."
Dunham is feeling particularly reflective as Girls comes to a close. During a TimesTalks panel on Wednesday night, the actress revealed that she made out with a guest actor during the HBO series' first season.