Oracle – how add milisecond to a timestamp value?

Recently somebody needed to add a millisecond to a timestamp value in Oracle. You can’t do just

 select systimestamp + 1 / 24 / 60 / 60 / 1000 from dual; 

because the ‘+’ converts timestamp to date and fractional seconds are lost. The (supposedly) wise guy here seems to suggest that the way to go is to create a custom function in Java… Come on Oracle, there should be a better way to do this!