Examples include an apparatus for generating a three-dimensional object. The apparatus comprises at least one energy source, at least one build layer temperature sensor, and a controller. The controller is to control the at least one energy source to pre-fuse a portion of a build layer in a build area when a build layer temperature is less than a first temperature threshold. The controller is further to, after pre-fusing the portion of the build layer, control the at least one energy source to fuse the portion of the build layer in the build area when the build layer temperature is less than a second threshold.