‘The Housemaid’ Author Calls Sydney Sweeney Movie Version ‘Better Than the Book’

Freida McFadden is sharing her thoughts on the upcoming film adaptation of her novel, The Housemaid.

In a Sept. 16 Instagram post, also posted to the film’s official Instagram on Sept. 25, the bestselling author wrote an early review of the upcoming psychological thriller film, which stars Sydney Sweeney and Amanda Seyfried.

The Housemaid follows Millie Calloway (Sweeney), a woman who accepts a role as the housemaid to a wealthy couple. While under their employment, Millie comes to see the dark secrets that the couple — Nina (Seyfried) and Andrew (Brandon Sklenar) — are hiding.

“I was lucky enough to get to watch a sneak preview of The Housemaid movie, and I absolutely LOVED it!” McFadden captioned her post. “The second it was over, I turned to my husband in the theater and said, ‘Omg, I think it was better than the book!’ (And he said, ‘Yeah’).”

McFadden also teased that the film “captured everything that readers love about the novel.”

“And the performances by all the actors were nothing short of incredible,” the author continued. “It (almost) made me want to write another Housemaid book. (Almost!) The only problem is, I don’t know how I’m going to be able to wait until December to get to watch it again!”

The PEOPLE Puzzler crossword is here! How quickly can you solve it? Play now!

McFadden serves as an executive producer on the film alongside Sweeney and Seyfried. She is also the author of three other books within the Housemaid universe, including The Housemaid’s Secret and The Housemaid is Watching, among other psychological thrillers.

McFadden isn’t the only person praising The Housemaid’s screen adaptation either. Director Paul Feig spoke to PEOPLE during the SXSW Film & TV Festival in March, and noted how the movie’s team “did a really good job” at creating the novel’s film treatment.

“We had a great writer, Rebecca [Sonnenshine],” Feig said. “Because it’s nerve-wracking — like, it’s easy to make something out of a book that’s not good; when a book’s really good, it’s like, oh boy.”

Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories.

“So I was very attentive to it, Sydney [Sweeney] was very attentive to it, and I think we hit just the perfect balance.”

The Housemaid will be released in theaters on Dec. 19.