RCMP officers are warning holiday shoppers in Montreal to beware of fake $20 bills.

"It's fair to say that when you get a paper $20 bill right now, there's a good chance you can encounter a counterfeit one," said Daniel Michaud, head of the RCMP's counterfeit squad in Quebec.

Michaud says that while the new polymer $20 bills are almost impossible to counterfeit, copies of the old paper bills have been circulating recently in Montreal.

How to tell if it’s a fake

Police say there are a number of ways to verify a paper bill's authenticity.

When you tilt the bill, the metallic stripe — with numbers and maple leaves — should change colour.

A "ghost image" of the queen should appear when you hold the bill up to the light.

There should be thicker, raised ink on the large number “20” and on the text that says "Bank of Canada".

Michaud says if you think you're getting a fake bill, refuse to accept it.

"Once you accept the bills, you're stuck with them. You actually take 100 per cent of the loss from having accepted that bill,” he said.

Investigators are examining the fake bills they recovered recently for evidence.