/28 instead of /24

Hi All,

  Looking for some advice related to a customer whitelist request. We advertise a xxx.xxx.xxx.xxx/24 externally....a customer says this subnet range is too large and wants to use a /28.....My question is, since we are advertising /24 do I need to do anything on my side ( advertise a /28) or since they are accepting only /28 , the larger /24 will cover this?

Thank You,

            Ron C