Prime Minister Malcolm Turnbull says the Liberal candidate for the Longman byelection made an innocent mistake and is very embarrassed about falsely claiming to have a prestigious military medal.

Trevor Ruthenberg was forced to apologise to voters in the crucial Queensland seat after he falsely claimed to have a medal for distinguished service in peacekeeping and non-war operations.

He hopes voters will believe that he made a simple mistake in a biography he wrote about himself back in 2012.

He says he does have a lesser medal, recognising his service in the air force, and he simply wrote down the wrong medal name.

“I’m not a military impostor. I did serve in the military,” Mr Ruthenberg told ABC radio on Tuesday morning.

He later told reporters he’d also apologised to the defence community and to Mr Turnbull for any damage he may have done to the government’s chances of taking Longman from Labor at this month’s byelection.

“This is not the sort of front page news that the prime minister wants to see,” he said, but added he would not be pulling out of the race.

“I’m standing here saying that this is my fault, this is my mistake. I’ve apologised.”

Mr Turnbull said Mr Ruthenberg was a big, honest, patriotic guy and he accepted the candidate’s explanation.

“He misdescribed a medal he’d received for his service in the air force … As he said, he screwed up. He’s ‘fessed up but it was an honest mistake.”

Mr Ruthenberg said he was solely responsible for the error in his Queensland parliamentary biography, which was penned shortly after he was elected as part of Campbell Newman’s government.

The biography says he holds the Australian Service Medal, which is presented by the Governor-General on the recommendation of the Chief of the Defence Force.

In fact, he holds the Australian Defence Medal, which merely recognises four years of service.

Mr Ruthenberg said he would never intentionally claim to own a medal that he wasn’t entitled to, and local RSL presidents and Vietnam veterans had accepted his apology.

“All of them understood and acknowledged that it’s easy enough to make. And they all know me. They all know my integrity and my service.”

Mr Ruthenberg is trying to win Longman for the government, after Labor’s Susan Lamb was forced to quit the parliament over the dual-citizenship saga. She is recontesting the seat.