Unlike a prior conviction, a conditional stern warning cannot be factored in during sentencing for other offences, the High Court has clarified in a case involving a former undergraduate who molested his classmate and peeped at another student.

The 26-year-old had touched his 24-year-old classmate while she was asleep in April 2017.

This happened just two months after he was administered a conditional stern warning by the police for peeping into a bathroom cubicle at a 22-year-old undergraduate in November 2015. Both offences occurred on campus and all names were redacted in judgment grounds delivered last week.

Under the terms of the warning he received, the man was to ensure he did not commit any offence within 12 months of the warning being administered. But he did.

As a result, he was charged in court for the peeping offence as well as for the molestation offence.

When it came to sentencing him for the molestation offence, the district court took as aggravating factor the fact that he was serving a conditional stern warning for peeping.

In the judgment grounds, Justice See Kee Oon said the peeping offence cannot be taken as an antecedent as the man was "not charged, much less convicted and sentenced" for it until he was also charged for the outraging modesty offence.

He said the warnings are a signal that reoffending will lead to the accused person being prosecuted for the offence he had been warned for, and not as "discrete aggravating factors in sentencing".

The former student had pleaded guilty and was convicted in a district court last year for the peeping offence, for which he was sentenced to one month's jail. For the second offence, he received eight months' jail and three strokes of the cane. A third charge of criminal trespass was taken into consideration.

In the High Court appeal last month, the man's lawyer Tan Hee Joek had argued his sentences were manifestly excessive. Among other things, he said the district judge had erred in treating as an aggravating factor the fact that the man had reoffended while serving the 12-month conditional stern warning.

Mr Tan also called for caning to be set aside as precedents show caning is not always imposed even where private parts are touched.

Deputy Public Prosecutor Raja Mohan said the district judge had rightly considered that the appellant had reoffended two months after being given the warning, and had escalated from peeping to committing molestation.

Justice See partly allowed the man's appeal for the peeping and molestation offences.

He saw no reason to disturb the eight-month jail term for the molestation conviction, saying the aggravating factor of escalation in criminal behaviour was negated by the mitigating factor of early plea of guilt.

But he set aside caning, noting there was no skin-to-skin contact or prolonged contact in the molestation case. The victim was also not restrained by the man.

As for the peeping offence, Justice See said it was not premeditated and the offender was "suddenly overcome by an inexplicable urge to peep". The judge held that the threshold for a jail term for peeping was therefore not crossed and replaced the one-month jail sentence with a $2,000 fine.

He noted that the man had "an extremely strong propensity for reform" but pointed out that "deterrence outweighs rehabilitation in this case".

The former student, who has started serving his prison term, had his sentence changed on appeal to eight months' jail with no caning, and a fine of $2,000.