Lawful act duress is a fraught doctrine because it condemns lawful behaviour. It may invalidate the legal consequences of lawful behaviour, namely a contract. This article poses the question: how do we distinguish between lawful actions that do – and do not – amount to duress? In answer to this question, it is argued that the current definition of illegitimate pressure, propounded by the Supreme Court in Times Travel (UK) Ltd v Pakistan International Airlines Corporation, is question-begging. It would be better to define illegitimate pressure as a threat that does not correspond to the type of the transaction. This definition is relatively easy to apply and explains the case law. It would place lawful act duress on a sound footing.