Builders have discovered tonnes of bricks abandoned in the ceiling over the state dining room in Government House - supported only by temporary timber.
Thousands of dignitaries, including the Queen, have dined there in the past 50 years. The room has also been used for investiture and state luncheons.
Mike Hannaway, from the Department of the Prime Minister and Cabinet, says three-and-a-half tonnes of bricks from an old chimney were left in the ceiling at some point last century and discovered only last year.
Mr Hannaway says builders were shocked when they discovered the bricks. Had they fallen, he says they could have landed on the dining table, though it would have taken a big shake for the bricks to topple.