Mexico City subway users often complain about malfunctioning escalators that keep breaking down continually. In any given CDMX metro station, you’ll find that escalators are out of order more often than they are functioning. And city officials have offered an explanation that shocked no one—people are peeing on them so much that escalators are corroding. Yup, you read that right.

Of the system’s 467 escalators, 22 are out of service on any given day.

Travelers on the Mexico City subway system often blame authorities for broken-down escalators at subway stops, but Metro officials have another explanation. Somehow, urine is penetrating and corroding the drive wheels and mechanisms of the escalators that carry riders up from underground stations.

One-quarter of escalator breakdowns on the Mexico City Metro are caused by people urinating on them, according to authorities.

The deputy manager of mechanical installations, Fermín Rafael Ramírez Alonso, said that Tacubaya and Chabacano are among the most affected stations.

Maybe—just maybe— stop peeing on escalators?

Ramírez urged users not to urinate on escalators or other Metro installations, because of the damage it causes. “When we open up escalators for maintenance, there is always urine,” Ramírez said.

But another issue is that there are no public bathroom facilities available.

Most stations have no public bathroom facilities, a fact Twitter users were quick to point out, noting there are not even any pay toilets. “More than this being an issue about ethics or manners, I think that this is happening because of a lack of free and accesible bathrooms in the city,” tweeted one user.

Ramirez also said that other causes for breakdowns include excessively heavy loads, running on the stairs, imbalance on the stairs and objects falling between them.

“There are even users who cut the stairs with knives or other sharp objects, of which we have examples in Tacubaya,” he said, surprising absolutely not one of Mexico City’s users. Many metro users know that vendors even sell knives on subway carriages, as was noted by this tweet.

The biggest problem, subway authorities admit, is that many escalators are old, or have been damaged by rough use.

The city plans to replace about 55 escalators over the next two years. With over 1.6bn rides per year, the MexicoCity subway is considered the eighth largest in the world by some measures, and one of the cheapest: a 25¢ ticket will get you a single ride to any destination on the 140-mile (226km) system. Just remember to use the bathroom before setting out.