Expert judgment plays an essential role in assessing the safety of levees,since these very long structures are generally old, few data are availablefor them, and they are subject to complex failure mechanisms. Expertjudgement is required to assess the failure probabilities of levees when car-rying out risk analysis studies. However, expert judgement is subject tobiases that are highly likely to impair the quality of the probabilistic assess-ments obtained. This article presents a method for reducing biases inexpert opinion, illustrated by its application to the case of an existinglevee. Initially, the method comprises the calibration of the opinions of apanel of six experts based on the results of a quantitative analysis appliedto 30 levee cross-sections for which numerical calculations were performed.It then proposes a procedure to debias expert assessments using bias cor-rection coefficients. Regarding its application, the assessments made by theexperts were debiased for 30 calibration variables. The correction coeffi-cients obtained were then applied for the assessment of 10 variables ofinterest. The results show a significant reduction of biases, associated witha readjustment of the uncertainty intervals given by the experts.