The reflection of a dominant mode field at the junction of an air‐ferrite interface in a rectangular waveguide is investigated. A singular integral equation is derived for the interface electric field on the basis of the quasistatic approximation. The integral equation is solved by using a function‐theoretic technique. Closed‐form solutions valid for the entire range of medium parameters are developed assuming that the ferrite is entirely lossless. It is shown that these solutions can be made to satisfy the realness condition on the discontinuity reactance for the entire range of medium parameters. The above condition which can be proven directly on the basis of the Hermitian nature of the permeability tensor of the lossless ferrite was not satisfied by the previously published solution for a partial range of medium parameters. Finally, the modifications caused by the presence of the losses in the medium are discussed briefly.