From tomorrow, celebrants will have to read out a new monitum — a statement explaining the nature of marriage.

Previously civil celebrants would have to note that: “Marriage, according to law in Australia, is the union of a man and a woman to the exclusion of all others, voluntarily entered into for life.”

This will be changed to reflect the change in definition to “union of two people”.

Celebrants were only notified of the change on Friday morning and Civil Celebrations Network founder Rona Goold said this could cause confusion among those who had not seen the email sent by the Attorney-General’s office about 11am or other notices informing them of the change.

“Some people might not get the message,” Ms Goold said.

Another celebrant news.com.au spoke to said he was not sure whether he had to use the new monitum on Saturday as he hadn’t had a chance to read the emails.

But Ms Goold said couples could rest easy because their marriages would still be considered valid even if the celebrant used the wrong monitum.

“Their marriage will still be valid provided they are free to marry,” she said.

“Section 48 basically protects the couple from any mistakes celebrants make.”

The Governor-General Sir Peter Cosgrove signed off today on the Marriage Amendment (Definition and Religious Freedoms) Bill 2017 — the last step to making same-sex marriage legal in Australia.

This changed the legal definition of marriage in the Marriage Act 1961 from being a “union of a man and a woman” to a “union of two people”.

The change will take effect on Saturday but same-sex couples will have to give a month’s notice before they can marry.