One of England's oldest windmills is at risk of being lost forever, Historic England said.
Bourn Mill in Cambridgeshire has been added to government agency's Heritage at Risk Register.
The Grade I listed ancient monument dates from the 1600s but faces collapse due to its rotting central support beams.
The Heritage at Risk programme works with owners and organisations to find solutions to protect sites.
Archives show the mill was bought by a Thomas Cook in 1636.
The Cambridge Past, Present and Future heritage group, which owns the mill, believed the building was much older.
The main post of the mill is thought to be from a tree felled at some point after 1515.
Unlike a fixed windmill, Bourn Mill can be manually rotated on a central wooden post - allowing the sails to be turned directly into the wind.
The site was an inspiration for the work of architect Lord Foster, who would draw the mill while studying at Manchester University.
Experts found "significant decay" in the mill's supporting timbers and said "well-meaning" cement repairs in the 19080s enabled rainwater to infiltrate the ancient crossbeams.
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