Before you spend that dollar bill on a cup of coffee, you might want to take a closer look at it. Believe it or not, some relatively modern $1 bills are attracting serious attention from currency collectors, and it all comes down to a rather unusual printing mistake.

We're talking about a batch of $1 bills that were printed with duplicate serial numbers. The mistake involved two U.S. currency printing facilities, and collectors have been on the hunt for matching bills ever since.

Some matched pairs have sold for thousands of dollars. That means a dollar bill you might get as change could potentially be part of something much more valuable.

Here's what you need to know before digging through your wallet, purse, or that old jar of spare change.

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Why Some 2014 and 2016 $1 Bills Are Worth So Much Money

Normally, every U.S. bill has its own unique serial number. You shouldn't be able to find two legitimate bills with the exact same serial number.

However, a printing mistake involving the Bureau of Engraving and Printing created an unusual exception.

In 2014, the Bureau authorized certain $1 replacement notes to be printed at its Washington, D.C., facility. In 2016, overlapping serial number ranges were printed again at its Fort Worth, Texas, facility.

READ MORE: Some $2 Bills Are Worth Thousands. Here's What to Look For

Both groups of bills eventually made their way into circulation.

That meant two different $1 bills could have the exact same serial number, even though they were printed at separate facilities.

How to Identify the Valuable $1 Bills

Collectors are looking for a very specific type of dollar bill.

According to AOL.com, you'll need to check three things:

Series year: The bill must say Series 2013.
Federal Reserve seal: Look for the letter B inside the Federal Reserve seal on the left side of the bill.
Serial number: The serial number must begin with B, end with a star, and fall within one of the qualifying ranges.

The two qualifying serial number ranges are:

B00000001* through B00250000*
B03200001* through B09600000*

There's Another Important Detail to Check

Look at the face plate number printed on the front of the dollar bill. Notes printed in Fort Worth have a tiny "FW" marking. Bills printed in Washington, D.C., do not have that marking.

This small difference helps collectors determine where each bill was printed.

The goal is to locate two bills with the exact same serial number, one printed in Washington, D.C., and the other printed in Fort Worth.

How Much Are These Duplicate Serial Number $1 Bills Worth?

According to currency collecting reports, matched pairs have sold for hundreds of dollars and, in some cases, more than $25,000.

READ MORE: Your $5 Bill Might Be Worth $2,000, Here's How to Find Out

The final value depends on several factors, including the condition of the bills, their serial numbers, and demand.

A pair with lower serial numbers or bills in really good condition could be more valuable.

How to Find Out If Your Dollar Bill Has a Match

One of the best known resources is Project 2013B, a collector website dedicated to documenting these duplicate serial number bills and helping people connect with others who own matching notes.

You can visit Project 2013B to learn more about the printing error, check the serial numbers, and find information about registering a potentially qualifying bill.

So the next time you're handed a $1 bill at a store in Lafayette, Broussard, Youngsville, or anywhere else in Acadiana, take a second to look at it.

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There's never been a better reason to sort your pocket change!

Gallery Credit: Credit: Mateo, 103.5 KISS FM