Prime Minister Malcolm Turnbull says he has "full confidence" in Revenue Minister Kelly O'Dwyer, after a number of blunders in Parliament this week.

Ms O'Dwyer accidently supported a motion condemning the Government on Wednesday, and then was unable to answer a question about the same bill yesterday.

But Mr Turnbull has told Melbourne radio station 3AW she's doing a good job, adding that Ms O'Dwyer had acknowledged that she "slipped up".

"I have full confidence in Kelly," he said.

"She's very, very capable... As one of the saints said, 'To err is human'. And, so, we all make mistakes."

The Opposition used Thursday's Question Time to capitalise on the Coalition's mistake, with one question on Ms O'Dwyer's "brilliant career" being ruled out of order.

The Revenue Minister was later unable to answer a specific question about the bill at the centre of yesterday's incident, prompting jeers from Labor MPs.

The series of bungles follows last month's mistakes, when the Government lost three consecutive votes in the Lower House after a number of Coalition MPs left early.

Justice Minister Michael Keenan was among them, but the Prime Minister said he still had confidence in Mr Keenan, who was also present for this week's mistake.

"I have full confidence in all of my ministers," Mr Turnbull said.

"The moment I cease to have full confidence in a minister, of course, they cease to be a minister."

A number of senior Coalition ministers have spoken in support of Ms O'Dwyer, but Manager of Opposition Business Tony Burke said Wednesday's error was not her first mistake.

"Let's not pretend for the Minister for Revenue that last night [Wednesday] was the only offence," he said.

"This is a person who designed the Census, this is the person who contradicted the Prime Minister over negative gearing."