Amazon has issued a voluntary recall of six AmazonBasics portable battery chargers due to overheating, The Verge reports. The power banks, sold between December 2014 and July 2017, have a risk of overheating, causing them to melt, which could cause a fire hazard. The report says the recall is being done in partnership with the US Consumer Product Safety Commission, although a recall notice hasn’t been posted to their website yet. It’s unclear if the power banks have caused any injuries or fires thus far.

The recall affects six models of power bank, the 16,100mAh, 10,000mAh, 5,600mAh, 3,000mAh, 2,000mAh with Micro USB cable, and 3,000mAh with Micro USB cable. Those are model numbers B00ZQ4JQAA, B00LRK8JDC, B00LRK8IV0, B00LRK8I7O, B00LRK8EVO and B00LRK8HJ8. All affected devices have already been removed from sale on Amazon’s website.

Amazon is reportedly emailing users who bought the power banks to inform them of the recall, and provide more information about how to return the devices and get a refund. You shouldn’t just mail the power bank back to Amazon in a box; judging by how the recall of Samsung’s infamous Galaxy Note 7 went, you’ll need to ship any potentially defective devices back in a special fireproof box.

Amazon doesn’t manufacture the AmazonBasics electronics products itself, but rather rebrands devices made by a third-party manufacturer. In this case, Gizmodo reports the power banks were made by Guoguang Electric Company Ltd. in China. Medium-capacity power banks often use several standard 18650 lithium-ion batteries connected together, and those batteries are made by a handful of large factories.

Fortunately, there are about a million more power banks on Amazon right now that won’t catch fire.