Amazon is issuing refunds for those who’ve purchased possibly fake solar eclipse glasses on the site in anticipation of this summer’s big solar eclipse event.

A lot of folks have been gearing up for the event that will — depending on where you are — either totally block out the sun or partially block it as the eclipse moves across the North American hemisphere on August 21st. Many of these same people have turned to the ease of Amazon for ordering the protective eyewear needed to look directly up at the sky while the solar phenomenon passes overhead.

However, Amazon has not been able to verify all of the glasses on its site have come from reputable manufacturers and, as first reported in the Verge, has now sent out a safety warning, telling customers not to use the questionable eyewear.

“Safety is among our highest priorities,” an Amazon spokesperson told TechCrunch about the matter. “Out of an abundance of caution, we have proactively reached out to customers and provided refunds for eclipse glasses that may not comply with industry standards. We want customers to buy with confidence anytime they make a purchase on Amazon.com and eclipse glasses sold on Amazon.com are required to comply with the relevant ISO standard.”

Reports of safety issues have been going on for a couple of months. One woman whom Amazon recently refunded, bought 500 eclipse glasses in bulk on the site from a Chinese manufacturer who told her they were safe. It was only later she learned the manufacturer had purposely misled her with a fake safety labeling.

It goes without saying, but improper eyewear could seriously damage the vision of those looking directly into the eclipse. “Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the Sun; they transmit thousands of times too much sunlight,” warns the American Astronomical Society (AAS).

Amazon has reportedly been shutting down shops offering unverifiable eclipse eyewear and issuing notifications not to use them in case they cause eye damage but it may be a little too late for some who don’t get the warning in time. We’re also right up to the edge of purchasing the proper glasses from the site in time for the eclipse for those without Prime.

Of course, there’s still a wide selection available to choose from on the site if you are looking to get a pair. But, look for a mark on the glasses with the ISO 12312-2 international safety standard before purchasing. These glasses are verified to block out all but 1/100,000th of the Sun’s light and can protect your eyes from harmful radiation while you enjoy the event.

Also keep in mind NASA and the AAS only recognize a short list of brands that meet the proper safety standards. Check out the full list of approved manufacturers here before buying online.

Those Amazon customers who did not receive a message from the company warning them of the safety concerns have purchased a product that was confirmed by the supplier to be ISO compliant, according to Amazon. Those concerned they may have a non-compliant product can still reach out to Amazon’s customer service for a refund under the A-to-z Guarantee.