Deutsche Postbank will commit to maintain an overcollateralisation level of at least 15% for its mortgage Pfandbriefe, above the legal minimum of 2%, the issuer said on Friday, a move an official at the bank said is aimed at retaining a triple-A Fitch rating of the covered bonds.

Postbank said that it made the voluntary commitment “to document that it will maintain in future the high quality of its mortgage covered bonds that exceeds the legal requirements of the German Pfandbrief Act”.

The commitment was published on its website on Friday, with Postbank committing to maintain voluntary nominal overcollateralisation (OC) of at least 15% in mortgage cover pool D.

The voluntary OC commitment comes just shy of three weeks after Fitch on 24 March placed AAA Postbank mortgage Pfandbriefe on Rating Watch Negative (RWN), saying this was because OC required for the triple-A rating increased and the issuer may not provide an OC commitment in time – “within the next three weeks”. (See here for previous coverage.)

An official at Postbank told The Covered Bond Report that the issuer made the commitment to keep the Fitch AAA rating of the mortgage Pfandbriefe.

The commitment will be reviewed at least once a year. Any changes to the commitment will be made public “in an appropriate form” at least four weeks before they take effect, said the issuer.

The last time Postbank tapped the benchmark market was in February 2011, with a Eu1bn 10 year mortgage issue. Fitch considers the programme to be dormant given the issuer’s lengthy absence from the market.