NASA is warning that some of the paper solar glasses being distributed to view the upcoming total solar eclipse are not safe.

The agency says you need to check your glasses for two things – the ISO Icon. And be sure the glasses are made by a U.S, manufacturer – such as American Paper Optics, Rainbow Symphony, Thousand Oaks Optical or TSE 17.

NASA also says if the glasses are wrinkled or scratched, they won’t be safe. And if you have the glasses sitting around that your dad used to view that eclipse back in the 60s, those aren’t safe either. NASA says the glasses can only be used for about three years.