The electrical shielding of the sample which is inevitable for the measurement of high impedances can lead to significant anomalies in the measured impedance. The displacement current, which flows between the sample and the shield, can result in "inductive loops" appearing in the impedance spectra at low frequencies. Experimental results are presented and analyzed via a transmission line model. Finite element calculations confirm the considerations. The significance for impedance spectroscopy and solid-state ionics is discussed.