This paper starts from the presupposition that moral codes often do not suffice to make agents understand their moral responsibility. We will illustrate this statement with a concrete example of engineers who design a truck’s trailer and who do not think traffic safety is part of their responsibility. This opinion clashes with a common supposition that designers in fact should do all that is in their power to ensure safety in traffic. In our opinion this shows the need for a moral philosophy that helps engineers to interpret their responsibility and think more critically about it. For this purpose we will explore the moral philosophy of Alasdair MacIntyre, which is particularly interesting because he locates the beginning of moral thinking in the daily practice of a profession. This is consistent with the history of moral codes, for codes are also the product of moral reflection by professionals. We will use MacIntyre’s philosophy to (1) explain what is wrong with the designers’ understanding of their responsibility and (2) show a possible way to bring their reflection to a more self-critical level. We will also inspect MacIntyre’s proposal critically.