Whether hard-adaptive measures (for example, seawalls) actually reduce vulnerability to natural hazards is the subject of considerable debate. Existing quantitative risk assessments often ignore behavioural feedbacks that some claim lead to increased development in hazardous zones. Here, we couple a tsunami model with a land-use change model and find that hard-adaptive measures can induce a false sense of security and inadvertently lead to increased vulnerability (that is, are maladaptive). We also observe that heightened hazard awareness (a type of soft-adaptation) can reduce vulnerability. Our results have two major implications: (1) they challenge existing hazard adaptation practice by quantitatively demonstrating the potential for hard-adaptive measures to be maladaptive, and (2) they highlight that ignoring the behavioural feedbacks in hazard assessment can alter the conclusions to the extent that they fail to identify maladaptive actions. In addition to the demonstrated case of tsunamis, the result may be relevant to other, repeatable natural hazards where urban growth influences exposure (for example, storm surge). Ultimately, neglecting future urban development and the temporal evolution of risk can result in incorrect conclusions regarding adaptation strategies; including these processes is therefore an essential consideration for the natural hazard and climate change impact communities.