The Philippines’ top court heard arguments on Tuesday for the legalisation of gay marriage, a historic first in the overwhelmingly Catholic nation. Two same-sex couples denied licences to wed urged the Supreme Court to strike down a 1987 law that states marriage must be between a man and a woman.

“When the right to marry, a decision so personal, so intimate and so life-changing, is denied to LGBT people, the state is not valuing their dignity,” lawyer Jesus Falcis, who is also a co-plaintiff, told justices in Manila.

It took three years for the Supreme Court to schedule a hearing and the case is likely to move at a glacial pace. However the plaintiffs may have an ally in President Rodrigo Duterte, who has expressed support for gay marriage but since backed away from a campaign pledge to legalise it.

“I am for same-sex marriage. The problem is, we’ll have to change the law. But we can change the law,” Duterte told a gathering of LGBT people in his southern home city of Davao in December last year. Falcis told the South China Morning Post that while Duterte “has not done anything concrete towards making same-sex marriage a reality ... his pronouncements create a more conducive environment to talk about same-sex marriage”.

“The Speaker of the Lower House Pantaleon Alvarez is [Duterte’s] ally in Congress,” Falcis said. “Alvarez filed bills proposing civil unions. While I personally don’t support such [a] label, it’s a step towards legalisation of same-sex marriage. I don’t think Alvarez would have done that without backing or a go signal, explicit or implicit, from Rodrigo Duterte.”

Judges will next hear from the government’s lawyers, but the court does not set itself deadlines to issue rulings and cases sometimes take years to resolve.

Legal experts say the case is still highly significant.