The Melanesian Spearhead Group secretariat says last-minute changes to the wording of the MSG constitution agreement allowed for all countries to be accommodated.
The signing for the first formal MSG constitution took place in Vanuatu last Friday.
Fiji was included in the signing came despite earlier representations by MSG leaders that its military-backed interim government had been told it wouldn't be able to sign.
However, the wording of the agreement's preamble, relating to the signatories, changed from government to state.
The chairman of the secretariat, Johnny Koanapo, says MSG leaders had already decided to include Fiji before changes were made to the preamble.
And he denies suggestions that Australia or New Zealand may have had input into the shape of the agreement.
"The agreement is driven by the members of the Melanesian Spearhead Group with no formal input from any of the development partners. But we understand the important principles that are normally included in such agreements. And as much as it can this agreement tries to take these principles into account and it was enshrined in the constitution."