For just 20p, plucky McDonald’s customers can enjoy extra sauce, another Oreo cookie, more Crunchie or even more Dairy Milk pieces.
All McFlurry fans have to do is ask their server, and they will be happy to make the addition.
But this trick has not previously been well known, so now fans are taking to social media in droves to spread the word.
It has come to light customers can even mix and match toppings – although no-one is sure how many extras it is possible to get.
McDonald’s have said the extra toppings are only available in certain stores, depending on whether the individual franchise is happy to offer it.
But judging by the locations of those sharing their special McFlurry’s on social media, the trick is available worldwide.
A spokesman for the fast food giant in the UK said: “We offer guidance around pricing, but ultimately our franchisees decide on those which are set based on a number of factors.
“We and our franchisees pride ourselves on providing good quality food at affordable prices up and down the country, and work to keep differences to a minimum.”
The 20p extra toppings are not the only cheeky extra McDonald’s fans can get their hands on.
Customers buying their new Signature Collection burgers may also get a Julien Macdonald designed box.
The Julien Macdonald boxes will be in a limited run of 1,000 and only available at a series of McDonald’s showcase events around the UK.
One special box, embellished by Julien himself, will be unveiled at McDonald’s Leicester Square restaurant, and opportunities will be explored to donate proceeds of its auction to the Ronald McDonald House Charities.
At the unveiling of his creation for The Signature Collection at the restaurant’s Leicester Square branch, Julien revealed how he developed the box’s design.
He said: “It’s something that is kind of fun and supposed to make people happy. I’ve done lots of collaborations but I’ve never done a food collaboration.
“I’m a huge fan of McDonald’s, my mum goes once a week, it’s like her weekly treat, and I went as a little boy. It’s very accessible to people and I like that about it.
“The design of the box is very very glamorous, very glitzy, a bit rock ‘n’ roll and shows my love of metallic and baroque – things that are quite over the top.”