A life tip from Gerard Butler: Don’t rub phosphoric acid on your face. The actor found that out the hard way when he accidentally wiped the substance on his visage while filming a climatic scene for Plane.

Appearing on Late Night with Seth Meyers (via EW), Butler explained how the accident happened while shooting Plane in Puerto Rico. His character, Brodie Torrance, goes hands on to fix an aircraft’s faulty brakes.

“Now I’m sticking my hand in between these two wheels, kind of pretending that I know what I’m doing,” Butler told Meyers. “Every time I bring my hands out, they’re covered in blood and green fluid, right? And I’m like, ‘I don’t know what this green fluid is.'”

Quickly, Butler found out the substance was basically phosphoric acid. Even worse, because of the heat in Puerto Rico, he used his covered hands to get rid of the sweat on his forehead. “I’m rubbing my face and, suddenly, it’s in my throat,” he said. “It’s in my mouth. It’s up my nose. It’s in my eyes. It’s burning my face, and I mean burning.”

While it was painful, Butler laughed while saying the incident was great for the scene. He’s okay now and promoting Plane, which premieres tomorrow, January 13. Butler is joined in the film by Mike Colter, Yoson An, Daniella Pineda, Paul Ben-Victor, and Remi Adeleke.

Butler’s character, Brodie, is an airplane pilot who must team up with an accused murderer, Louis Gaspare (portrayed by Colter), on a war-torn island. The pair end up there together after Brodie assists in an emergency landing after flying through a lightning storm.