Electrochemical impedance measurements performed on gas-evolving electrodes in high-conductivity solutions have shown artefacts at high frequency (HF) when using a commercial reference electrode (RE) due to its relatively high impedance. A "trick" consisting in coupling a platinum wire in series with a capacitor of 0.1 mu F to the standard RE, hence making a dual RE, has been used for a long time without a clear understanding of how it works. This paper investigates HF EIS measurements in high-conductivity solutions from experiments in 1 M H2SO4 solutions and simulations based on the equivalent circuit of the cell and of the electrode potential measurement device. In particular, the value of the capacitor and the position of the platinum wire are considered. Curiously, while the HF artefact is removed by the dual RE, a spurious loop may appear at low frequency depending on the position of the platinum wire. This is explained from simulations based on the equivalent circuit of the cell. (C) 2011 Elsevier Ltd. All rights reserved.