A former security guard who forced his then 15-year-old daughter to perform oral sex on him was sentenced to 10 years and four months' jail on Wednesday.

The four-month term was imposed in lieu of caning as the man, now 50 years old, cannot be caned.

The High Court heard that the victim, an only child, lived with her parents in a flat with one bedroom.

She usually slept in the room with her mother, while her father slept on a sofa bed in the living room.

One night in late 2016, the girl accompanied her father to drink beer at a nearby void deck.

When they returned home, she lay on the sofa bed to text her friends, as she did not want to disturb her mother, who was already asleep.

Shortly after, her father joined her on the sofa bed. She asked him to lull her to sleep by patting her thigh or arm, as he had done many times before.

However, this time, he slipped his hand under her T-shirt and started rubbing her waist.

She moved away and told him not to come close to her, but he pinned her down and tried to kiss her.

He told her to keep quiet as she continued to protest, then forced her to perform oral sex on him.

After he fell asleep on the sofa bed, the girl did not raise the alarm. She wanted her parents to remain together and was mindful that telling her mother about the incident would cause them to break up.

The next day, her father asked her whether she had enjoyed the night.

She rebuked her father for behaving the way he did, given that she was his daughter.

In 2017, the girl was placed in a welfare home after her father threatened her with a knife. There, she found out that she was not alone as some of her hostel mates had also been sexually assaulted.

She finally told her mother on Jan 21, 2018, about what her father had done to her. The woman informed the girl's child protection officer and a police report was made.

The man was arrested on Jan 24, 2018.

Yesterday, he pleaded guilty to a charge of sexual assault by penetration.

Prosecutors sought at least 11 years' jail for the offence and an additional four months' jail in lieu of eight strokes of the cane that the man would have received, based on sentencing guidelines, had he not been 50 or above.