If Scott Morrison heeds the advice of his departmental chief, the treasurer won't be squandering any revenue windfall the federal budget might receive from a surge in commodity prices.
Treasury secretary John Fraser on Wednesday told a Senate committee it was unclear how much of the recent surge in coal and iron ore prices were driven by temporary or more persistent factors, presenting difficulties in preparing the budget.
"If these elevated prices continue, we should prioritise budget repair and ensure any additional revenue is banked as an improvement to the budget bottom line," he said.
"We need to take great care not to fall into the trap of spending unexpectedly higher revenue should it arise."
Mr Morrison later told reporters it was "very good advice", noting there were some months before Treasury has to finalise its commodity price assumptions for the May budget.
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Mr Fraser said global rating agencies - Standard & Poor's, Moody's Investors Service and Fitch Ratings - had sent a clear warning on the nation's debt, although it was a message they say that about every country.
"We are not Robinson Crusoe in that regard," he said.
Speculating on what the agencies may or may not do with Australia's triple-A rating was "possibly a fool's errand".
But Mr Fraser believes what has happened since the mid-year budget review in December has probably been beneficial to the budget with the rise in commodity prices.
However, he is at odds with International Monetary Fund head Christine Lagarde who recently warned of a risk to the global economy from a race to the bottom in cutting company taxes.
"I don't see it as a race to the bottom for a key reason - governments in the end have to fund their spending," he he said.
Finance Minister Mathias Cormann says Australia is nowhere near the bottom when it comes to corporate tax.
"We are getting closer and closer to the top," he told the hearing.
Even if parliament legislates the government's 10-year tax cut plan, Australia would only be middle of the road among OECD countries.
US President Donald Trump told a joint session of Congress his economic team is developing historic tax reforms that will reduce the tax rate on US companies so they can "compete and thrive anywhere and with anyone".
"It will be a big, big cut," he said.
Under Australian government's $50 billion tax plan, the corporate rate will be incrementally lowered to 25 per cent.
Companies presently pay 30 per cent, apart from those with a turnover of under $2 million which are taxed at 28.5 per cent.
Mr Morrison linked slow wages growth to the need for corporate tax relief.
"You don't get people higher wages by taking profits ... by making it harder for businesses to be profitable and earn the income which pays wages," he told ABC radio.
Mr Morrison conceded wages growth over the past few years had been "very, very modest" and that was frustrating everybody.
