If you have any $1 bills in your wallet or under your couch, you might want to think twice before using them.

This is because currency collectors in the U.S. are willing to pay up to $150,000 for some versions of the dollar bill with a particular printing error.

According to Wealthynickel.com, some dollar bills printed in 2014 and 2016 feature a mistake from the US Bureau of Engraving and Printing that could make them worth $150,000 by collectors.

Here’s everything you need to know:

How many of these $1 bills are in circulation

According to the Bureau of Engraving and Printing, a total of 6.4 million banknotes were printed with the error in 2014 and 2016.

The federal bank in New York issued one batch while the second was issued in Washington D.C., though the bills could be anywhere in the world at this point.

How to identify if your $1 bill is worth thousands

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

• The Series date located on the far right of the photograph of George Washington must read “Series 2013”
• The bill has a “B” Federal Reserve Seal above the serial number located to the right of Washington’s photo
• The serial number ends with a star (★) and fall between B00000001★ – B00250000★ or B03200001★-B09600000★

If your bill has these characteristics, you must now find the the other one from the matching pair with the same serial number.

How many matching $1 pairs have been found

To date, only nine pairs with matching serial numbers have been found, meaning millions are still in circulation.

A matching pair can reach between $20,000 and $150,000 depending on the condition, according to WealthyNickel.

If you believe you have a matching bill, you should take it to a local coin shop to inspect and appraise it.

Why are they worth so much

According to The American Numismatic Association, a congressionally chartered nonprofit dedicated to the study and collection of bills and coins, currency misprints are extremely rare, making them extremely valuable among collectors.