(4)In line with Principles 1 and 4 of the guiding principles for supervisors set out in the BCBS standards, it is necessary to ensure that institutions do not apply the derogations as an economic choice that maximises their profits through the selection of alternative high quality liquid assets based primarily on yield considerations. In line with those principles it is also necessary to establish a mechanism for limiting the use of the derogations in order to mitigate risks of non-performance of the alternative assets. Taking into account the BCBS standards it is also necessary to provide for appropriate haircuts for the purposes of the derogation provided for in Article 419(2)(a) of Regulation (EU) No 575/2013 and to establish rules on the fee for the purposes of the derogation provided for in Article 419(2)(b) of that Regulation. In particular, as regards the derogation provided for in Article 419(2)(b) of Regulation (EU) No 575/2013, in order to ensure that the price paid by an institution for a central bank credit line is fair, the fee should be composed of two elements. The first should offset the higher yield earned on the assets kept to secure the credit line in order to ensure that the pricing reflects benefits which accrue independently of the amount currently drawn. The second should reflect the amount of the credit line drawn down.