A child was killed in an accident involving a Peloton treadmill, the fitness company’s CEO said in a letter posted on its website.

In the letter, CEO John Foley said he “recently learned about a tragic accident involving a child and the Tread+, resulting in, unthinkably, a death.” He stressed the company’s focus on safety when designing and building products, but encouraged customers to take precautions, such as keeping the equipment’s safety key out of reach of children and making sure space around the treadmill is clear.

“While we are aware of only a small handful of incidents involving the Tread+ where children have been hurt, each one is devastating to all of us at Peloton, and our hearts go out to the families involved,” he said.

Foley declined to provide further details about the treadmill accidents in the letter, citing families’ privacy.

Peloton, best known for its stationary bike, has surged in popularity during the Covid pandemic as more Americans look for ways to stay in shape at home. The company has struggled to keep up with such high demand and recently said it would invest in its supply chain to shorten wait times. During the pandemic it has added a pricier bike and cheaper treadmill to its lineup. It recently teamed up with Adidas for an exclusive apparel line — another indicator of its growth and large customer base.

According to NBC News, the Consumer Product Safety Commission, a federal watchdog agency, is aware of the incident and investigating.

Treadmill deaths are rare, but injuries are relatively common. An estimated 22,500 treadmill-related injuries were treated at emergency room in the U.S. in 2019, the most recent year of data available, CPSC spokeswoman Patty Davis told NBC News. About 2,000 of those involved children under age 8, she said.

Seventeen fatalities associated with use of a treadmill were reported to the CPSC between 2018 and 2020, including a 5-year-old child.