"We've already made adjustments to Loan-to-Value Ratio (LVR) restrictions to partially manage this risk, but we haven't seen a sufficient reduction in risky lending."
The Reserve Bank said it would consult on making the LVR rules even tighter "in order to prevent this problem from getting worse".
It is proposing halve the amount of high LVR lending to owner occupiers - meaning lending more than 80 per cent of the value of a property - to 10 per cent of all new home loans.
The new rules could be in place from October.
The announcement of changes to LVRs came as Robertson and Reserve Bank governor Adrian Orr struck a deal over new lending tools.
"I have largely agreed to the Treasury and Reserve Bank's proposed update to the [memorandum of understanding] to add debt serviceability tools, but as I indicated in June this extension should not unduly impact first home buyers," Robertson said in a statement.
An amendment to the agreement states that in "designing and implementing a debt serviceability restriction, the Reserve Bank will need to have regard to avoiding negative impacts, as much as possible, on first home buyers," according to Robertson's office.
"I believe this agreed wording will set clear public expectations while maintaining the operational independence of the Reserve Bank," Robertson said.
"It is still up to the Reserve Bank how it chooses to introduce any restrictions, having had regard to this condition."