Prosecutors have lodged an appeal against mushroom killer Erin Patterson's sentence on the grounds the judge "erred" when he considered the triple murderer's time in solitary confinement.

The Office Of Public Prosecutions Victoria on Monday filed an appeal against Patterson's prison sentence handed down last month.

Patterson was handed three life sentences for the murders of Heather Wilkinson, Don Patterson and Gail Patterson, and 25 years for the attempted murder of Ian Wilkinson, with a 33-year non-parole period.

Prosecutors have lodged an appeal on the basis there was an error in the sentence imposed and that it was "manifestly inadequate".

"The sentencing judge erred in finding that there was a 'substantial chance' the respondent would be held in 'solitary confinement for ye

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