In certain examples, a method comprises determining a fusing area density distribution of a build layer from build data relating to a build layer of a three-dimensional model to be printed by an additive manufacturing system. The method comprises, in response to a determination that a region of the build layer has a fusing area density outside of a fusing area density tolerance window, modifying the build layer to define a build layer in which the region has a fusing area density that is within the fusing area density tolerance window.