"But if we face the prospect of a "meaningless process" rather than a "meaningful vote", Parliament will be enraged".
So just hours after the concession, (or non-concession) very, very dark mutterings began from those who had been persuaded by what they thought was a promise.
These were the words of a minister expecting to win the vote.
MPs in the House of Commons will vote on a string of amendments to a key piece of Brexit legislation that could force the government's hand in the negotiations with the European Union.
Some lawmakers tried to shout him down and accused the government of wanting too much power.
May is resisting changes approved by the House of Lords that would soften Britain's exit from the European Union, because she says they will weaken the government's negotiating position.
The former attorney general told Press Association: "The Prime Minister agreed that the amendments we had tabled, and the issue that we had raised about Parliament's role in the event of no deal was an important one, and undertook to work with us to put together amendments to present in the Lords which would address those concerns".
Davis warned lawmakers the government would never allow them to "reverse Brexit" and called on them to back its own amendment, which proposes a 28-day breathing space if parliament rejects a Brexit deal, during which the government would have to make a statement on its plans.
In the tense atmosphere where it was not clear which way the vote would go, the government secured its victory only after offering concessions to one of the leaders of a group of Conservative lawmakers who were threatening to vote against May.
Following a meeting with Theresa May, Tory MPs said they had been promised "input" into what the government would do if the United Kingdom faced a no-deal scenario.
Liberal Democrat Brexit spokesman Tom Brake said: "As has become a tradition in Brexit negotiations, the Tories have been forced to cobble together a compromise".
"We must under all circumstances respect the result of the referendum", Brexit Secretary David Davis told lawmakers as he opened the debate.
This came after a last-minute resignation by the justice minister Dr Phillip Lee, who said he could no longer look his children in the eye and vote to support the government.
The battle now moves to the House of Lords, where the government will formally reveal how much it has conceded in the wording of a new amendment expected on Monday or Tuesday. May's Cabinet is divided between ministers including Foreign Secretary Boris Johnson, who support a clean break with the European Union, and those such as Treasury chief Philip Hammond who want to keep closely aligned to the bloc, Britain's biggest trading partner.
But May won a key vote in parliament on Tuesday with a compromise on plans to give lawmakers a "meaningful" vote later this year on the terms of Britain's exit from the EU.
If May is defeated in the House of Commons it will be yet another blow to a prime minister whose authority has been challenged several times since last year's election.
Theresa May saw off a revolt from the pro-European wing of her fractured party, averting what could have been a major political crisis.