Colleen Hoover is defending the casting of It Ends With Us, the film adaptation of her blockbuster 2016 novel, People magazine reports.

At Book Bonanza, her annual literary fair in Grapevine, Texas, Hoover responded to fans upset by the actors chosen for the lead roles in the film.

Hoover’s novel, which follows Lily, a businesswoman who falls for Ryle, a neurosurgeon, but soon learns that he’s abusive, became a huge bestseller after readers on TikTok embraced it. A critic for Kirkus gave the book a starred review, writing, “Packed with riveting drama and painful truths, this book powerfully illustrates the devastation of abuse—and the strength of the survivors.”

Some readers were upset that the role of Lily, who is 23 in the book, will be played by Blake Lively, 35, and that Ryle, 30 in the novel, will be portrayed by Justin Baldoni, 39.

“Back when I wrote It Ends With Us, the new adult [genre] was very popular,” Hoover said. “You were writing college-age characters. That’s what I was contracted to do. I didn’t know that neurosurgeons went to school for 50 years. There’s not a 20-something neurosurgeon.”

She said that she asked the filmmakers to “age them out” in the film. She also predicted readers would enjoy the movie, saying, “You guys are going to be so happy. I’m extremely happy and now my expectations are up and I’m going to keep them there.”

The film version of It Ends With Us, written by Christy Hall and directed by Baldoni, was in production until earlier this month, when it was paused due to the Writers Guild of America strike.

Michael Schaub, a journalist and regular contributor to NPR, lives near Austin, Texas.