Mexico's Supreme Court ruled Thursday that a law allowing same-sex marriages in Mexico City is constitutional, rejecting an appeal by federal prosecutors who argued it violated the charter's guarantees to protect the family.

The justices' 8-2 ruling handed a legal victory to hundreds of same-sex couples who have been married in Mexico's capital since the landmark law took effect March 4. When approved last December, it was the first law in Latin America explicitly giving gay marriages the same status as heterosexual ones, including adoption.

The court, however, must still rule on the adoption clause and whether the ruling will affect states outside of the capital. It is expected to address adoption on Monday.

"We are very happy," said Mexico City lawyer Leticia Bonifaz, who argued Mexico City's case. "It fell to us to carry to a conclusion a struggle that has taken a long time."

Justices who voted on the majority side stressed that while Mexico's constitution enshrines protection for families, it does not define what a "family" is.

"It does not appear to me to be unconstitutional," Justice Jose Gudino said during Thursday's session. "The concept of the family established in the constitution ... is an open concept."

Jaime Lopez Vela, a leader of the group Lesbian, Gay, Transsexual and Transgender, was among a group of activists who celebrated the ruling outside the court.