An eyecup insert is provided which allows easy attachment and removal of an eyecup from an associated night vision goggle. The eyecup provides a light secure seal when pressed against the head of an operator of the goggle. A connecting end of the eyecup has annular channel which engages the insert. The insert is ring shaped with a central aperture having a plurality of detents protruding inwardly of the aperture. The operator can form a snap-fit connection between the eyecup and the goggle by forcing the aperture over a circular flange which surrounds an eyepiece of the goggle until the detents have snapped passed the flange. The eyecup can be removed by reversing the installation procedure.