Levi’s owners are checking the tags of their jeans after it was revealed that some of the company’s vintage garments are worth a whopping $33,000. Jeans made by the brand between 1949 and 1954 are selling for astronomical amounts online, and there’s an easy way to date the denim.

Levi’s jeans have become a staple in everyday fashion for many consumers. And if you have a pair sitting in your closet, you may want to check the tag.