In the modern era, going to work doesn’t necessarily mean showing up to an office. It might mean working remotely from an Airbnb halfway across the world from company HQ, or it might be knocking out emails at home at 9 p.m.

Being able to choose when and where you work is a luxury, but it comes with a price, as new research shows. Having more autonomy in your work often means working longer hours, even when controlling for seniority and different job types.

“Greater flexibility and autonomy over work sound great—and could well herald a new era of better work-life balance,” University of Kent sociologist Heejung Chung writes in The Conversation. “But so far much of the evidence points to the opposite,” she warns.

Chung recently published a study in the European Sociological Review that examines work-schedule data from the German Socio-Economic Panel, a national survey that interviews 12,000 German households and 32,000 people a year. She and co-author Yvonne Lott of the Hans-Böckler Foundation in Germany looked at workers who were fully employed and said they had flexible work hours in 2003, 2005, 2007, 2009, and 2011.

The study analyzed the difference between what happens when men are given flexible schedules at work and when women are, but it found that regardless of gender, people who have more leeway in their work schedule tend to work longer hours. They hypothesize that this could be because people view flex time as a gift from their employer, and work hard to show that they deserve it; or because there are fewer boundaries between work and the rest of your life when you don’t have set office hours.

The researchers did find a difference between men and women who have control over their own schedules, though. Men who gain more control over their work schedule work more hours, but also tend to get paid more, while women don’t get a financial reward for putting in more time.

As important as work-life balance is, flexible schedules can be more exploitative than helpful, this research shows.

[h/t Quartz]