There is provided an x-ray detector having a number of x-ray detector sub-modules. Each detector sub-module is an edge-on detector sub-module having an array of detector elements extending in at least two directions, wherein one of the directions has a component in the direction of incoming x-rays. The detector sub-modules are stacked one after the other and/or arranged side-by-side. For at least part of the detector sub-modules, the detector sub-modules are arranged for providing a gap between adjacent detector sub-modules, where at least part of the gap is not directed linearly towards the x-ray focal point of an x-ray source.