Specifically, he had trouble learning to use his character's whip.
"I wasn't talented at it, but I got there in the end," he told Variety. "It's really like fly-fishing."
Dornan, 32, stars alongside Dakota Johnson, 25, in the film, which is set to hit theaters on Valentine's Day. The film's director, Sam Taylor-Johnson, claimed that ultimately, Dornan's new-found handiness with a crop did lead to (minor!) injuries for Johnson.
"I'd have to remind Jamie to hold back," she said. "I think there was a bit of rope burn."
Still, Taylor-Johnson insisted that the film isn't just sex. Fans should also expect to see a complex tale of a couple navigate their relationship.
"On the early draft, there was a sense that there was way too much sex," she said. "The story, of course, is of equal importance. We tried to balance the narrative correctly, so one doesn't feel like it's drowning the other."