For some bonds, such as in the case of TIPS, the underlying principal of the bond changes, which results in a higher interest payment when multiplied by the same rate. For example, if the annual coupon of the bond were 5% and the underlying principal of the bond were 100 units, the annual payment would be 5 units. If the inflation index increased by 10%, the principal of the bond would increase to 110 units. The coupon rate would remain at 5%, resulting in an interest payment of 110 x 5% = 5.5 units.