(CNN) -- Sweden's parliament on Wednesday approved same-sex marriage legislation, according to the parliament's Web site.

Previously, two people of the same sex could register their partnership, but with this vote, sex will no longer matter when two people want to get married.

The new "sex-neutral" law will take effect on May 1.

Couples who already had a registered partnership can now either stay in that union or transform it into a marriage if they wish, the Web site said.

The "yes" votes numbered 261, while 22 members of parliament voted "no" and 16 chose not to vote.

The Christian Democrats was the only party opposed to the new law.

"Unfortunately this is not an April Fool's Day joke, this is reality," Yvonne Andersson, member of the Swedish parliament for the Christian Democrats, wrote on the party's Web site following the vote.

The party had instead proposed a law that would remove the word "marriage" from Swedish law and replace it with a legally binding union between two persons, thus separating it from the Christian ceremony that the church conducts.

Asa Regner, secretary general of the Swedish Association for Sexuality Education, told CNN that Wednesday's vote meant a very important change in Swedish law.

"This was the last area where same sex couples were treated differently," she said.

All About Sweden • Culture and Lifestyle • Same-Sex Marriage