Iraq's parliament has reversed its decision to change the rules governing a referendum next week on the country's new constitution.
The constitution is seen as crucial to fulfilling US plans for Iraq
The altered rules would have made it much harder for Sunni opponents of the draft constitution to reject it.
Parliament has now decided to revert to the original rules - as both the United Nations and Washington said it should.
UN legal advisors said that a referendum held under the new rules would not meet international standards.
After a brief debate, MPs voted 119 to 28 to restore the original voting rules for the referendum.
Only about half of the 275-member body attended the vote, although a quorum was achieved.
The parliament is dominated by an alliance of Shia religious and Kurdish parties who support the new constitution.
On Sunday they voted that the two-thirds majority needed in three provinces to defeat the constitution would be counted from all registered voters, rather than actual voters.
That would have made it much harder to vote down the new charter, especially as turnout could be very low in areas where there may be fighting or intimidation.
At the same session, however, parliament ruled the 50% hurdle that had to be crossed to ratify the constitution would apply only to those who actually voted - not those registered.
The UN said the parliament decision - to define the word "voters" in two ways in a single sentence - was unacceptable and would not meet international standards.
Sunni Arab leaders had reacted angrily to the amendments to the rules, saying it was a fix to prevent their people from getting a veto under the old rules.
"A resolution was passed that the word 'voters' ... was voters who are registered in the voter lists and who exercise that right, i.e. that they vote in the referendum," deputy speaker Hussain al-Shahristani told reporters after Wednesday's vote.
The parliament has, however, insisted on conditions which correspondents say have the overall effect of asserting parliament's legal right to challenge the outcome.
The conditions include posting security forces in dangerous areas, vetting polling station staff and the right to challenge results which had been distorted by intimidation.
"The government is completely keen to make the constitutional process legitimate and of high credibility and we are concerned about the success of this process rather than the results of the referendum," said government spokesman Leith Kubba after the vote.
UN officials have begun distributing 5 million copies of the new constitution to voters across Iraq ahead of the 15 October vote.