If you have a few $1 bills lying around, you could be sitting on hundreds of thousands of dollars.

Thanks to a U.S. Bureau of Engraving and Printing error, two batches of $1 bills printed in November 2014 and July 2016 could now be worth up to $150,000 a pop.

According to the personal finance site Wealthy Nickel, the request for the first batch was sent to a Washington, D.C. printing facility in 2014, but the same request was somehow also made in July 2016 and printed in Fort Worth, Texas. This resulted in bills with duplicate serial numbers being sent into circulation before the error was noticed.

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There are an estimated six million pairs of the bills currently in circulation, though only nine pairs have been matched back together to date.

According to USA Today, currency collectors are willing to pay anywhere from $20,000 to $150,000 for a pair of the erroneous batches.

If you’re the lucky owner of one of the bills, the “Series” date (which is next to the photo of George Washington) will say “Series 2013” with a “B” Federal Reserve Seal above and a serial number ending with a “*” symbol. The range will fall in between B00000001* – B00250000* or B03200001*-B09600000*.

Related: Quarters From One U.S. State and Year Could Be Worth a Lot

If you believe you own one (or a pair) of the bills, you can submit it to an online database called Project 2013b, which attempts to catalog all of the misprinted bills and eventually match them all together.

To date, over 36,000 bills have been cataloged.