The construction of the provisional equidistance line – the first stage of the three-stage maritime delimitation procedure espoused in the decisions of international courts and tribunals – is examined by contrasting the ideal of an objective, geometry-based provisional line with the actual practices of simultaneity and preemptive modification of baselines. Examples are presented from the case law of the International Court of Justice and other international courts and tribunals with respect to the selection of appropriate basepoints from which to construct the provisional line, a practice which introduces relevant circumstances and a significant level of subjectivity to the first-stage of the delimitation process. This practice has the potential to undermine the legitimacy of maritime boundary decisions.