Assessment reliability can be affected by various types of unforeseen events. In any such circumstances where a concern is raised that the reliability of assessment is lower than usual, our natural inclination is to allow extra leniency in grading to reduce the chances of students missing out on a grade they deserve. This article shows how, by focusing on the risk for individual students, we might logically approach this situation in deciding exactly how much additional generosity is required. In particular, it shows how making progress with this problem requires an acceptance that no assessment system is perfect and transparency about the level of reliability that is achievable. Having developed an approach, this article also shows how this may lead to different outcomes than the competing desire to maintain assessment standards so that the group of students in question are not unfairly advantaged relative to previous and future cohorts.