Approximate expressions are obtained for the field produced when an electromagnetic plane wave is diffracted by an arbitrary angled dielectric wedge, whose refractive index is near unity. The solution is obtained from an application of the Kontorovich–Lebedev transform and a formal Neumann–type expansion. The diffraction problem is solved by firstly solving a related wedge diffusion problem and then using analytic continuation to obtain the solution for the diffraction problem. The results have applications in diffusion and wave propagation into a wedge.