Grain boundary engineering plays a major role for controlling the properties of modern high-performance materials. Especially Mo and its alloys have advantageous high-temperature structural properties as well as a number of attractive functional properties. However, depending on the processing state, technically pure Mo is prone to intercrystalline failure at low temperatures. The addition of B and/or C is known to improve interface cohesion, allowing for a targeted improvement of mechanical properties through segregation engineering. In this work, the early stages of crack initiation of technically pure and B micro-doped Mo are investigated by scanning electron microscopy on the tension-loaded surface after three-point-bending of mm-sized specimens. Increased grain boundary cohesion is evident from a drastically reduced relative length of separated interfaces in the B-doped material. The presence of B at the grain boundaries is confirmed via atom probe tomography experiments.