A man who repeatedly raped, bashed and degraded a young woman over six weeks in a hotel room has had six years added to his prison term by Victoria's highest court.

Alfio Anthony Granata on Monday had his jail term increased to 23 years for keeping the woman as a sex slave in a room in the Rydges Bell City complex in Preston between November 2012 and Christmas Day of that year.

Granata, 49, was last year jailed for 17 years, and to serve 13 years before he became eligible for parole, but the Director of Public Prosecutions said the sentence was manifestly inadequate and took the case to the Court of Appeal.

The Court of Appeal on Monday found that initial term "did not adequately reflect the horrific nature of these rapes" and that the sentence did not "adequately reflect the need to denounce and punish the objective gravity of the offending".

The finding by Court of Appeal Justices Robert Redlich Robert Osborn and Chris Maxwell means Granata must serve 17 years in jail before he is eligible for parole. He has already served more than 1200 days in custody.