For investigation of diffusion, such experimental setup geometry arrangement is preferred, where as soon as possible homogeneous concentration field takes place in flat material samples. However, lateral mass transfer may play significant role. Here, this effect was solved for twodimensional diffusion through a layer of finite thickness to a circular target with an insulating ring. Simple formula has been suggested fitting the numerical results in a wide range of variables including asymptotic cases as well. The formula is suitable for determination of permeability using data received by electrodiffusion measurement under the conditions of limiting diffusion current to a circular electrode with a guard ring. (c) 2013 Elsevier Ltd. All rights reserved.