More 'very long term' bonds may be heading down the public sector borrowing pipeline, with the treasurer, Scott Morrison, airing concern over bond rollover risk.In a speech to the Australasian Finance and Banking Conference yesterday, Morrison said "lengthening issuance may increase the Commonwealth's cost of borrowing, but it decreases the risks of managing the debt portfolio."Rollover risk, which is the risk that existing debt will not be refinanced once that debt becomes due, has been reduced with the Commonwealth Government progressively extending the maturity of its borrowings over recent years.In mid October 2016 the Australian Office of Financial Management issued a new 30-year bond line (maturing in March 2047). This, Morrison said, "brought Australia into line with other major sovereign issuers and followed a gradual lengthening of both the nominal and real yield curves over recent years."