National Australia Bank has taken the unsual step of refunding A$590m ($565m) to investors that took part in a bond sale that was finalised only days before the bank stunned the market when it disclosed additional provisions of A$830m against its portfolio of collateralised debt obligations.

The Australian bank said it had agreed to the refund, which sees the amount raised from the June 2011 bonds cut from A$850m to A$260m, as a “gesture of goodwill”.