Pseudo-translational and pseudo-rotational modes are low-frequency but not necessarily the lowest ones, and moreover, more than six modes may have pseudo-translational and/or pseudo-rotational character. These normal modes are not well described, and there is thus a need to identify those most affected so they can be filtered out. The practice of projecting out translation and rotation as part of the vibrational analysis for molecules in a vacuum is invalid within the PHVA approximation. Instead, we introduce a simple scheme to identify the problematic modes and quantify the pseudo-translational and/or pseudo-rotational character.