We all know a dollar doesn’t go as far as it used to. But, if you have two $1 bills with the same printing error, you could find yourself sitting on a great big stack of cash.

According to WealthyNickel.com, coin and currency collectors are willing to pay up to $150,000 for rare $1 bills with particular printing errors from the U.S. Bureau of Engraving and Printing.

Here’s what happened:

In November 2014, the Bureau of Engraving and Printing requested a batch of dollar bills from its Washington, D.C. facility. Two years later in July 2016, the exact same request was sent to the bureau’s Fort Worth facility, WealthyNickel reported. The duplicate request led to the $1 bills being printed with the same serial numbers, despite coming from two different printers.

Typically, every bill has its own unique serial number. However, the misprint means there are 6.4 million pairs of matching $1 bills with identical serial numbers. Only nine matching pairs have been found to date, according to WealthyNickel.

The misprints weren’t caught and the bills were put in circulation. Collectors are on the hunt to find matching pairs of dollar bills and are willing to pay big for the prized finds. Experts estimate a pair could bring in between $20,000 and $150,000, depending on the numbers and condition.

According to WealthyNickel, here’s what you need to look for:

• Located near the image of George Washington should be a series date that reads “Series 2013.”
• The bill must have a “B” Federal Reserve Seal above the serial number.
• The serial number must end with a star and fall between B00000001* – B00250000* or B03200001*-B09600000*

Lucky enough to find a matching pair? You can read more on what you should do next here.