A cathode assembly including certain features designed to protect the integrity of a filament contained therein is disclosed. In particular, the cathode assembly is configured to prevent damage to the filament should it inadvertently contact another portion of the cathode assembly. In an example embodiment, an x-ray tube incorporating features of the present invention is disclosed. The x-ray tube includes an evacuated enclosure containing a cathode assembly and an anode. The cathode assembly includes a head portion having a head surface. A slot is defined on the head surface and an electron-emitting filament is included in the slot. A protective surface is defined on the head surface proximate to a central portion of the filament. The protective surface in one embodiment is composed of tungsten and is configure to prevent fusing of the filament to the protective surface should the filament inadvertently contact the protective surface.