Victoria's Court of Appeal found the original minimum six-year sentence handed to the man, who cannot be named, was manifestly inadequate.

He pleaded guilty in 2018 to four charges of incest against the girl, starting when she was just six years old.

The abuse, in her own bed, continued two or three nights a week until she was about 12.

He would sneak into the girl's room and assault her through the nights. As she grew older he would climb in bed with her while naked.

The judges said the stepfather took on "the role of a boyfriend who needed (the girl)" when she was 12 or 13, and would tell her he enjoyed the girl's company more than her mum's.

He became jealous when she started seeing a boy at school when she was 14.

He pressured her to agree to more sex acts, threatening to leave her mother or kill himself if she didn't.

"The sexual conduct continued after (she) knew it was wrong, as she didn't know how to get out of it," the judges said.

The man also admitted sexually penetrating the daughter of a family friend during a sleepover at his home.

The girl was aged between 13 and 15 and sleeping in the daughter's bedroom when the man came in during the night and assaulted her.

Appeal judges Chris Maxwell and David Beach re-sentenced the man to 12 years behind bars.

He must serve a minimum of nine before becoming eligible for parole.

Australian Associated Press