Last week, the What it's REALLY like inside the world's biggest Primark store opened in Birmingham inside a former shopping centre.
The new branch, which cost a whopping £70 million, has got a Disney café, a hair salon and all the Harry Potter-themed clothing you could ever dream of.
Clearly, a lot of work went in to making the shop as exciting as can be - but one customer recently noticed that a small but awkward blunder had been made when the finishing touches were being added.
And it's all to do with Primark's free water dispensers, which are dotted around the five-floor, 160,000 sq ft building.
But can you work out what's wrong with them?
What it's REALLY like inside the world's biggest Primark
In a now-deleted tweet, a chemistry teacher from south west England shared a photo of one of the water dispensers she saw.
Above the machine, there's a message on the wall for customers informing them that H2O is "on the house".
But something's not quite right about the text.
Alongside the photo, the teacher wrote: "I think there is a love-hate relationship between Primark and the formula of water.
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"Surely not many people spotted the mistake. #YouHadOneJob."
She's talking of course about the error in the scientific formual for water.
On the wall in Primark, the formula uses a number zero instead of the letter O.
The O in H2O stands for one oxygen atom, and thus is represented by a capital letter.
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Many of the teacher's followers were baffled by the post and couldn't spot anything wrong, but a few people worked it out.
One person decided to take things further and joked that due to the incorrect formula, the dispenser must give out free hydrogen gas.
They wrote: "So technically it dispenses hydrogen gas? Risky stuff..."
To which the teacher replied: "Oh didn't think about that! And what about that zero then? Could it be a subscript? H20? A superscript? Degrees? Oh the questions."
