JAKARTA (Reuters) - Indonesian groups pushing for an increase in the minimum age for girls to marry, from 16, said on Thursday it was encouraged by a Constitutional Court order that legislators should work on a change.

Indonesia, the world’s biggest Muslim-majority country, is among the top 10 countries in the world with the highest number of child brides, according to campaign group Girls Not Brides.

“We now have the legitimacy, that the decision of the Constitutional Court today strengthens and agrees with our reasoning,” said Lia Anggie, a legal representative for the coalition of campaigners against child marriage.

The coalition had petitioned the court on the grounds that the law discriminated against girls, who can marry at 16, while the legal age for men is 19.

Indonesia’s top court ruled that the government must change the minimum age at which a girl can get married. It did not specify an increase, and gave legislators three years to decide what the new minimum age should be.

Anggie told Reuters the court decision was “a clear step” in its push for ending child marriage.

While girls are legally allowed to get married at 16, it is common, particularly in rural areas for girls, to become brides at much younger ages.

One in four girls marry before they turn 18 in Indonesia, according to the U.N. Children’s Fund. On average, more than 3,500 Indonesian girls are married every day.

In its verdict, the court agreed that the marriage law discriminated against girls, a court spokesman said, adding that the law was also seen as out of line with rules on child protection.

The court had therefore found the law “unconstitutional”, spokesman Fajar Laksono said.

The court gave legislators three years to come up with a change, and in their deliberations, they should “take into consideration and see changing times”, Laksono told Reuters.

Erasmus Napitupulu, another legal representative of the group that filed the petition, which includes women who were child brides, said he welcomed the ruling but was disappointed the court “was not brave enough” to take a clear stand.

“Now the ball is in the hands of President Jokowi,” he said, referring to President Joko Widodo by his nickname.

“We will continue to push until women in Indonesia get protection and guaranteed rights from the state.”