Travis Perkins has been fined £2m following the death of a customer at its Old Wolverton branch in Milton Keynes. The company pleaded guilty at Amersham Crown Court to two offences under the Health and Safety At Work etc Act 1974.
The merchant was also ordered to pay prosecution costs of £114,812.76.
The customer, Mark John Pointer, 44, from Leighton Buzzard, was loading planks of wood onto the roof rack of his Land Rover when one of the cargo straps he was using snapped. He fell to the ground, where he was run over by a Travis Perkins vehicle that was operating in the yard. Mr Poynter died from crushing injuries after the accident, which took place in November 2012.
Judge Justin Cole, who sits at Aylesbury and Amersham Crown Courts, said it "was an accident waiting to happen".
Milton Keynes Council, which investigated the case, said the company had "failed to ensure loading and unloading activities were undertaken in a safe manner in a safe area".
John Carter, chief executive of Travis Perkins, said: "It's with deep regret that we acknowledge the conclusion of the court hearing regarding the tragic incident that occurred in 2012. Our thoughts continue to be with the family of Mr Pointer.
"Minimising the risks for everyone working in and visiting our challenging environment is my responsibility, and I take it very seriously. Safety will remain at the top of our agenda; we will continue to apply the lessons learnt from this terrible event with the aim of ensuring that an accident such as this never occurs again."