Vic judges mishandled incest case: Libs

Victoria's "defective" baseline sentencing reforms meant a father got less than seven years for incest with his teenage daughter, but the Liberal opposition insists the laws are workable.

Four Supreme Court justices dismissed an appeal against the father's short sentence and blamed the faulty laws.

The Director of Public Prosecutions had wanted to increase the sentence on the grounds that the sentencing judge erred in interpreting baseline sentencing.

But Justice Chris Maxwell said the problem was with the legislation, not the interpretation.

"The baseline sentencing provisions are incapable of being given any practical operation," he said on Tuesday.

Shadow attorney-general John Pesutto says the reforms the previous government introduced are workable despite the Court of Appeal ruling they contain an "incurable defect".

"I respect the majority's decision, but I also respectfully disagree with it," Mr Pesutto told reporters.

"The law, we believe, works appropriately."

The government is seeking urgent advice from the Department of Justice, Attorney-General Martin Pakula said.

"We want to come up with a solution in which those who have to apply these laws have confidence," Mr Pakula said.

The opposition have promised to provide bipartisan support for amendments to ensure baseline sentencing works as planned.

Mr Pesutto says the courts need to remember the reforms were introduced in response to community concerns about low minimum sentences.

The father - who can't be named for legal reasons - was sentenced in July to a maximum of six years and eight months prison under new legislation that set a median prison sentence for some serious offences.

The reforms increased the median sentence for incest with a minor to 10 years.

But the justices who dismissed the appeal found the new laws did not allow courts to calculate future median sentences.

As a result, the sentencing judge could not "scale up" sentences for incest, which is what the DPP argues should have happened.

The dissenting Court of Appeal justice in favour of the appeal found baseline sentencing provisions could work as a "guidepost".

The Law Institute of Victoria, which last year criticised the laws for their potential to result in unjust sentences, says the legislation does not work and is overly complex.