Unexpected costs have driven up the price of restoring one courthouse and building another in central Wellington.
The Government will spend an extra $12 million on restoring the historic 19th century High Court building in Stout Street and building a new Supreme Court.
The overall cost of the project is now more than $77 million.
Courts Minister Rick Barker says the restoration has required far more work due to water damage to the roof timbers, plaster features and brick work.
Higher material costs and a tight construction market in Wellington has affected progress on the Supreme Court.
Work on the buildings is expected to be completed late next year.