The Sirius building on the fringe of The Rocks will remain standing for some time yet, after the government's plans to demolish the building and use the money raised on alternative housing were defeated in court on Tuesday.

Acting judge of the Land and Environment Court Simon Molesworth ruled that former heritage minister Mark Speakman, now the state's attorney-general, made two errors of law when deciding not to list the building on the State Heritage Register.

The decision, which was greeted with cheers by community campaigners in a packed court room on Tuesday, means that new Heritage Minister Gabrielle Upton will have to redo a decision as to whether to list the building.

As such, the decision does not save Sirius, a building that has stoked fierce passions both for and against. But Shaun Carter, the president of the Save our Sirius group that has been fighting to preserve the brutalist structure, called on Premier Gladys Berejiklian to reconsider its future.