Former prime minister Kevin Rudd says it's too early to judge the long-term effect of the mining tax.
On Tuesday he said the minerals resource rent tax had not collected "any real revenue of any significance", as the government faced pressure to amend its design.
But on Wednesday, Mr Rudd told ABC Radio in Adelaide that while the tax receipts had been marginal in the first six months, there was "still a way to go".
He said it was also a situation of waiting to see what happened to the future of commodity prices.
"I think six months into a new taxation regime that only came into effect in the last year, is probably too early to judge its long-term effect," Mr Rudd said.
"Let's wait and see."
Mr Rudd also defended the government's borrowing levels, saying "what we have done is what every responsible government in the world has done".
Opposition leader Tony Abbott and others were putting about a "great lie" about Australia having an unsustainable debt level, he said.
Rather, it had one of the lowest, if not the lowest, in the world.