An Ivy League professor says his flight was delayed when a fellow passenger mistook his scribbling on a math problem as a sign he might be a terrorist.

American Airlines confirms that a woman expressed suspicions about University of Pennsylvania economics professor Guido Menzio.

He was flying from Philadelphia to Syracuse on Thursday to give a talk at Queen’s University in Ontario, Canada. He was working on a differential equation, but said he was told the woman thought he might be a terrorist because of what he was writing.

Casey Norton, a spokesman for the air carrier, said the women’s allegations about Menzio were deemed not credible.

Norton told The Washington Post the woman had initially told the flight crew she was too ill to take the flight but when she deplaned to take another flight she disclosed that the reason she was feeling ill was her concern about Menzio.

Menzio told the paper the woman was his seatmate on the flight.

The Post reported Saturday that the professor is a 40-year-old award-winning economist from Italy.

Menzio told the paper he was troubled by the women’s ignorance as well as “a security protocol that is too rigid—in the sense the once the whistle is blown everything stops without checks—and relies on the input of people who may be completely clueless.”

The 41-minute flight took off more than two hours after its scheduled departure, the Post reported, citing flight-tracking data.