A petrol bomb was launched into a Stantonbury shop while four people were inside on Saturday evening.
Tara Singh Kandola, 55, extinguished the fire after a glass bottle containing accelerant was thrown through the open front door of the Costcutter shop in Purbeck at around 6.20pm.
It hit a shelving display, causing fire and smoke damage to the floor.
There were two customers in the shop at the time, as well as Mrs Kandola, but no one was injured.
Mr Kandola, who has worked in the shop for 23 years, said: “We had the doors open because it was too hot when someone threw in a petrol bomb.
“The alarms were going off and I could see the fire, so I picked up the fire extinguisher straight away and managed to put it out.
“I was really frightened.”
Mr Kandola had put the fire out before crews from Great Holm and Newport Pagnell arrived.
He told the MK Citizen today he has installed cameras outside the shop to try and deter any future attacks on his shop and admits “that’s part of life”.
He added: “You have to just get on with it because people do silly things, they don’t think about the effect it will have on other people.
“We have to keep an eye out now to make sure nothing happens again in the future.”
If anyone was outside the shop or in the area at the time and saw anything that could help the investigation, please call investigating officer Det Con Greg Hughes from Milton Keynes Force CID on 101.
If you don’t want to speak directly to the police you can contact Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
No personal details are taken, information is not traced or recorded and you will not go to court.