The New Plymouth District Council has missed out on tens of thousands of dollars after it failed to collect rent from the country's largest concrete supplier - for 30 years.
The bungle means Firth Industries has not paid for its council-owned Fitzroy depot since its lease expired in 1986, despite continuing to operate there.
A commercial real estate agent, who asked not to be named, said the 4200 square-metre site would fetch about $53,000 a year at today's prices.
New Plymouth District Council property manager Peter Handcock said the gaffe was a result of the local body amalgamations in 1989 and came to light when Firth applied for a new long-term lease.
"The lease lapsed and it wasn't brought to the attention of the current council until about a year ago. At the time Firth Industries was looking at redeveloping the land, and they realised they didn't own it."
The council this week voted against offering Firth a new lease, but Mr Handcock hopes to have a new proposal ready by the end of the month.
Firth has declined to comment.