When building a bit-true retargetable compiler, every signal type must be implemented exactly as specified, even when the word-length of the signal does not match the length of the available hardware. Extra operations must be introduced in the algorithmic description in order to ensure that the remaining bits do not in$uence the databits and to assure that signal types are correctly converted from one type to anothe~An algorithm will be presented which generates code to assure bit-trueness, optimised for the available hardware.