A police officer only realised he had been shot after finding a bullet in his mouth, days after being involved in a 12-hour armed stand-off in the village of Sutton St James, Lincolnshire, last week.
The unnamed officer was taken to hospital after the police car in which he was travelling was fired at in the village of Sutton St James, Lincolnshire, last week.
He was one of two unarmed officers who initially attended the home of Barry Stephen Horspool following reports of a man with a firearm on 3 February.
A spokeswoman for Lincolnshire Police said the bullet found in the officer's mouth was being examined by ballistics.
"We're not sure what weapon it originated from but I've been told it wasn't a pellet from a shotgun."
During the Lincolnshire siege, armed officers were later deployed to the scene from Lincolnshire, Nottinghamshire and Leicestershire.
Police forces and residents of the sleepy village near the Norfolk border were asked to stay indoors while they dealt with the incident.
After attempts to negotiate with Mr Horspool, police later entered the property and found him dead in an upstairs room at 10.30pm.
She said it was initially thought the officer had been injured by glass from the car window, which had shattered.
But when doctors examined him in hospital they found the bullet in his mouth.
"I've not seen it but it can't have been a large bullet otherwise he would have realised. It is currently being looked at by our ballistics team whose findings will help form part of our investigation into the incident".
The spokeswoman confirmed the officer was treated and discharged on the same day.
She also denied reports that officers had been attending the property on Chapelgate to seize Mr Horspool's shotguns.
A cause of death has still not been revealed for the 61-year-old, who is thought to have lived with his wife Barbara and had a grown up daughter with two children who regularly came to visit the house.
An inquest into his death is expected to be opened and adjourned in Spalding later this week.
The incident was referred to the Independent Police Complaints Commission (IPCC) which said its initial assessment found Lincolnshire Police had done what they could to negotiate a peaceful resolution and a formal investigation was not necessary.