Megan Fox Is So Funny on 'New Girl' That 'It's Hard to Keep a Straight Face,' Max Greenfield Says

"We've been having so much fun," Max Greenfield tells PEOPLE

Photo: Getty (2)

When it comes to being the new New Girl, Megan Fox has been a perfect roomie, says costar Max Greenfield.

“Oh my God, so great!” Greenfield told PEOPLE at The Big Short‘s Hollywood premiere on Thursday. (Fox has been filling in for a portion of the fifth season during leading lady Zooey Deschanel‘s maternity leave.)

Greenfield, who plays uptight ladies man Schmidt, said he and his fellow cast members have been impressed with “just how wonderful she is to work with. We’ve been having so much fun. She’s very funny – I’m excited for people to see how funny she is. She’s been really good on these episodes. We’ve all really gotten along. She kind of fit in seamlessly. She’s done like four [episodes] so far, and it’s been really nice. We have a really good time.”

While Deschanel’s Jess is sequestered on jury duty, allowing the real-life new mom time at home with new daughter Elsie Otter, Fox’s character Reagan – described as “a gorgeous, straight-shooting pharmaceutical sales rep” – moves into Jess’ space in the apartment and shakes up the already uproarious dynamic among series regulars Greenfield, Jake Johnson, Lamorne Morris and Hannah Simone.

Greenfield, 35, says he’s enjoyed watching Fox, 29, reveal her considerable comedic chops.

“She’s very dry, and she’s very grounded in a lot of her material,” he said. “So it allows my character and Jake’s character and Lamorne’s character to really go for it and be big, and then she looks at you like, ‘What is wrong with you?’ It makes our stuff so much funnier. Then she will then like take another jab at you. It makes that secondary jab so cutting. It’s hard to keep a straight face in those moments.”

RELATED VIDEO: Check Out Megan Fox’s Beauty-to-Bombshell Transformation

With Fox making such a big impression behind the scenes, might she stick around even after Deschanel’s return? “I don’t know, I certainly wouldn’t mind it,” said Greenfield.

Meanwhile, when the show makes its midseason return, Greenfield’s Schmidt will find much of his storylines dominated by the wedding planning that follows his engagement to Cece (Simone) in the fourth season finale.

“That’s a season-long situation,” he said. “He’s going to get real deep into that one. It’s going to get ugly.”

New Girl returns Jan. 5 at 8 p.m. ET on Fox.