The reflectivities and transmissions of the first two Laguerre-Gauss modes incident on a Fabry-Perot interferometer are calculated and compared. It is shown that, dependent on beam-waist size, the Fabry-Perot interferometer can behave as a spatial filter. For example, the reflectivity of the TEM00mode can be larger than for the TEM01mode. This could allow for fundamental mode selection in a laser without resorting to an intracavity aperture.