This article was inspired by the UCL ‘Contract Law and the Unexpected’ conference on 16 May 2025 (Conference). At that conference a paper was presented which argued that material adverse change (MAC) clauses are similar to force majeure clauses and deal with uncertain events, but often with insufficient clarity. In this article we look at whether conventional MAC clauses in facility agreements are fit for purpose, and what that purpose is. We also look at a hybrid approach which creates a contractual renegotiation obligation when there is a change which may have a material adverse effect on the business or operations of the Borrower but falls short of being likely to cause a financial covenant breach or insolvency. This is also considered in the context of the debate about the role of good faith in contracts and its application to debt financing arrangements.