A council appointed by Thailand's military rulers has rejected a controversial new constitution drafted after last year's coup.
A new committee must now be appointed to write another draft, further setting back elections.
The draft has been widely criticised, in particular a clause which enables a 23-member panel to take over government during a "national crisis".
The army ousted the elected government last year after months of unrest.
The 247-member National Reform Council on Sunday rejected the draft charter by 135 votes to 105, with seven abstentions.
Correspondents say that it met strong opposition on practically all sides of the political divide.
Another committee will have 180 days to write a new one, which will later be put to a nationwide referendum.
Analysis: By Jonathan Head, BBC News, Bangkok
So what caused the military-appointed National Reform Council to reject their own side's constitution, the fruit of nine months of labour?
Preliminary conversations with members of the council suggest a number of factors. Some say they wanted to give the new economic team appointed last month by Prime Minister Prayuth more time to improve the ailing economy. Others worried that hostility to the constitution would reignite political divisions in the country in the run-up to the referendum on the charter scheduled for January 2016.
So the timetable for a return to elected government is postponed to early 2017, but many people here expect it will slip back even further, some wondering whether Thailand can have an election before the end of the decade.
Perhaps the military wanted their charter to fail. The inclusion, at the last minute, of a military-dominated council that for five years could legally take over the government whenever it felt necessary, outraged even some who might have supported the charter, making rejection in a referendum all the more likely.
Then there is the elephant in the room - the looming royal succession, perhaps the most important moment in Thailand's modern history. With King Bhumibol so visibly frail, that could happen any day now. When it does, all talk of elections will be put on hold, possibly for years.
Until a new constitution can be drafted, the military government retains its substantial powers.
It had said elections could take place in late 2016, but analysts say the delay means 2017 is more likely.
Critics of the draft constitution say it would erode the power of political parties in favour of the army and prevent a genuine democracy from being established.
Thailand has seen numerous different constitutions since the end of the absolute monarchy in 1932.
For years the kingdom has been divided between pro-democracy parties that support former Prime Minister Thaksin Shinawatra, and an alliance of conservatives, including members of the military, the judiciary and royalists.
Mr Thaksin's allies have prevailed in every election since 2001, but have faced two coups and the removal of three prime ministers by the courts.