Come November, your fiction preferences might have a real-life impact on your choices at the polls. People who have read Harry Potter novels tend to have a lower opinion of Donald Trump, according to a new study—and the more books they’ve read in the series, the less favorably they view the Republican presidential nominee.

These findings held true regardless of a person’s political party, gender, age, level of education, or religious beliefs, says study author Diana Mutz, professor of political science and communication at the University of Pennsylvania’s Annenberg School for Communication.

The massive popularity of the series, by British author J.K. Rowling, made such research possible; more than 450 million copies of the books have been sold worldwide, and Mutz found that both Republicans and Democrats were equally likely to have read them.

To gauge people’s opinions of the controversial businessman-turned-politician, Mutz surveyed a nationally representative sample of 1,142 Americans. (In addition to Trump and Harry Potter, she also asked them about hot-button election issues such as waterboarding, the death penalty, and the treatment of Muslims and gay people.)

She found that each book people had read in the fantasy series lowered their evaluations of Trump by about two to three points on a 100-point sale. “This may seem small,” Mutz acknowledged in a press release, “but for someone who has read all seven books, the total impact could lower their estimation of Trump by 18 points out of 100.”

To a lesser extent, Harry Potter readership was also associated with a more positive attitude toward Muslim and gay people, and a more negative one toward questions about the use of torture and killing terrorists.

Mutz believes that the books’ message of tolerance and respect for each others’ differences may play a key role in influencing readers’ political views.

For example, she writes, Harry Potter advocates for oppressed house-elves and opposes the evil Lord Voldemort’s quest for “blood purity” among wizards. Trump, on the other hand, has called for a temporary ban on Muslims entering the United States, and made comments about minorities, including women, Mexicans, and disabled people.

The protagonists in Rowling’s books are also reluctant to use violence to settle disputes, she writes, while Trump has supported waterboarding and bombing terrorists’ families.

Finally, Mutz writes, “it may simply be too difficult for Harry Potter readers to ignore the similarities between Trump and the power-hungry Voldemort.”

The study will appear in a special election edition of the journal PS: Political Science and Politics. Mutz concludes—with obvious bias of her own—that she’s not sure if Harry Potter can “defeat Donald Trump” in this year’s election, but that her research raises hope that the values the book preaches could prevail.