It was a historic day for gay marriages at Parliament, but a rather less memorable one for two MPs who became embroiled in "a horrible misunderstanding" over whether one of them had made a joke about rape.

Green MP Holly Walker complained to Speaker Lockwood Smith after saying she overheard MPs joking before the start of a transport and industrial relations select committee meeting yesterday.

She wrote on Twitter: "I just love it when my fellow MPs make rape jokes when waiting for select committee meetings to start. rapeculture oldboysclub".

She declined to repeat the jokes - understood to be about the age of consent - or say who made them.

Later, National's Jami-Lee Ross contacted the Dominion Post to say: "I think Holly might have been referring to me."

He offered her his apology, which she accepted.

After the House had voted on the gay marriage bill, she said she would be emailing Dr Smith to withdraw her complaint.

Earlier, however, the Lower Hutt-based list MP said: "Jokes of this nature are not appropriate in any workplace. I think this incident highlights that it is still a bit of an old boys' club, and has a way to go in respecting women who work there and are elected."

Mr Ross, the MP for Botany, said: "I'm absolutely mortified that she's taken my comments in this way and I've been trying to contact her tonight to explain.

"I trust she'll understand - but, in the meantime, I've also offered my apology if she took offence, absolutely none was intended. I did not, and do not, make jokes about such serious issues, and this is all a horrible misunderstanding."

A spokeswoman for Dr Smith confirmed the Speaker's Office received the complaint.

- © Fairfax NZ News