Here’s a sobering concept: the bicycle helmet you’ve been wearing might not meet federal safety standards. You might assume, as many people do, that all bicycle helmets sold in the U.S. are required to meet the Consumer Product Safety Commission’s (CPSC) standards, but the reality isn’t as clear-cut.

Technically, helmets are required to meet those standards, but in the online retail world, many bicycle helmets, some of which are widely sold and purchased, do not meet those standards. Consumer Reports researchers alone identified 13 helmets that didn’t include a CPSC compliance label. And many of those non-compliant helmets were offered on some of the biggest online shopping platforms.

In short, be extra careful when you buy a bicycle helmet. But what exactly should you be looking for? Let’s find out.