Rock singer Melissa Etheridge says she'll marry her long-term partner Tammy Lynn Michaels before California's vote on same-sex marriages next month.

Making a date: Melissa Etheridge & Tammy Lynn Michaels

"Yes, we have four children and we're trying to find the right time… to go down and do it," she told US TV celebrity show Extra.

Etheridge, 47, has twins with Michaels and two children for her previous relationship.

The couple exchanged wedding vows five years ago in Malibu, but that union was not legally recognised.