The Government has introduced urgent legislation to fix an error that caused many beneficiaries to be underpaid by one day.
It's been happening for nearly 20 years and the bill introduced today means the shortfall won't be repaid.
According to the way the rules were written, benefits were supposed to start the same day a stand-down period ended, usually a few weeks after someone first applied.
Instead of that happening, benefits have been paid from the day after the stand-down.
"It has always been government policy that a benefit will commence the day after a stand-down," Social Development Minister Anne Tolley said.
"The legislative error was unfortunate."
The Social Security (Commencement of Benefits) Amendment Bill corrects the error with full retrospective effect to June 3, 1998.
It was reported earlier this month that some beneficiaries had successfully applied for back pay and had received payments ranging from $40 to $300.
They won't be affected by the bill.
It will be debated under urgency after the bill that allows deportees to be supervised has been dealt with.