A heroin trafficker appealed against the extra jail time he received in lieu of being caned, and had his appeal thrown out.
But the case gave the court the chance to deal with an important question of law, said Chief Justice Sundaresh Menon.
Should a convicted criminal be given extra jail time if he is spared the cane owing to medical reasons?
The prosecution argued for this to become the norm, barring special circumstances, and proposed two weeks' jail for every stroke of caning avoided.
But the High Court yesterday said that while the court may impose extra jail time in lieu of caning, that does not mean it has to do so.
Under the Criminal Procedure Code, when a prisoner is found medically unfit to be caned, the court may remit the sentence of caning or impose an additional jail term of up to 12 months.
The wording of the provision is open ended, giving the court the discretion to impose additional imprisonment, said Chief Justice Menon, delivering the decision of a three-judge court. Such discretion should be exercised only when there are grounds to warrant an additional jail term, he added.
"This approach will mean that in each case, the court should consider the circumstances that are before the court and then decide whether enhancement is called for," he said.
The court will give detailed grounds in due course.
Amin Abdullah, 48, had appealed against an extra 30-week jail term given in lieu of caning. His initial sentence was the mandatory minimum of 20 years' jail and 15 strokes of the cane for trafficking in 13.23g of heroin and possessing 0.27g.
Last year, a prison doctor certified him permanently unfit for caning owing to a rare spinal condition.
After the prosecution applied for the caning sentence to be revised, the district court imposed the additional jail term.
Amin, who did not have a lawyer, appealed, arguing that the extra 30 weeks was excessive. He said he knew of other inmates who, like him, were exempted from caning because of their medical conditions but did not get more jail time. "A term of 20 years is already heavy to me," he told the court yesterday.
The court that heard his appeal also included Judge of Appeal Chao Hick Tin and Justice See Kee Oon. Chief Justice Menon noted that Amin had received the minimum jail term. "Even with enhancement of 30 weeks' imprisonment, the sentence was on the low side and was certainly not manifestly excessive," he said.
Deputy Public Prosecutor Terence Chua had argued that imprisonment in lieu of caning would preserve the deterrent effect of the corporal punishment, and that Parliament intended for the courts to impose extra jail time for offenders who are medically unfit to be caned.
Also weighing in was Mr Benjamin Koh, who was appointed amicus curiae (Latin for friend of the court) to give an independent view.
He favoured a flexible approach weighing all the relevant factors in each case, and said the mathematical approach of two weeks per stroke proposed by the prosecution was "not ideal". He disagreed with the prosecution's arguments on deterrence, noting that would-be offenders would not know for certain if they would be spared caning until they were certified in prison.