A man in his 30s with no underlying health conditions was offered a Covid vaccine after an NHS error mistakenly listed him as just 6.2cm in height.
Liam Thorp was told he qualified for the jab because his measurements gave him a body mass index of 28,000.
He told BBC Radio 5 Live: "I've put on a few pounds in lockdown but I was surprised to have made it to clinically, morbidly-obese.
"It really made me rethink what I was going to do for pancake night."
NHS Liverpool Clinical Commissioning Group said occasional errors could happen.
Dr Fiona Lemmens admitted she could "see the funny side" but also recognised "there is an important issue for us to address".
"There are millions of GP appointments taking place every day and while we take care to make sure records are accurate, occasional data errors do occur."
Mr Thorp, 32, said he was surprised to be offered the vaccine so called his GP to check.
He was then informed he was in vaccine priority group six because of his weight. The NHS says a BMI of between 30 and 39.9 is classed as obese.
"Like most people, I've put on a few pounds in lockdown but I was surprised to have made it all the way to the clinically, morbidly-obese category," he said.
"Although my mum wasn't surprised by this. She said she'd noticed I'd put on a few and this was probably the wake-up call I needed."
It was only when he received a call back the following day that the mix-up became clear.
Rather than being listed at 6ft 2ins in height, he was registered as 6.2cm, which led to the error in his BMI.
"I'm a bit on the chunky side, I weigh a good 17-and-a-half stone so to combine that with the 6.2cm in height and you get a BMI of 28,000," said Mr Thorp, who is political editor at the Liverpool Echo newspaper.
"I felt a bit uneasy about it because I know - having reported on this extensively - how many more people should be ahead of me in the queue," he said.
Mr Thorp has now urged others who believe there has been a mistake to always check with their GP.
"I'd much rather somebody else who needs it earlier than me got that appointment," he said.
"I was completely cool with it. Mistakes are going to happen in such an enormous undertaking."