As an integral part of the International Temperature Scale of 1990 (ITS-90) the interpolating constantvolume gas thermometer (ICVGT) covers the temperature range between 3 K and 24.6 K. It requires calibration at only three fixed points without the application of explicit gas-thermometric corrections. Before the introduction of the ICVGT in 1990, computer simulations were carried out to establish to what extent the design parameters influence its behaviour, since the design details were to be left to the user. At the time only the major parameters were examined. One of the parameters not considered was the influence of thermal anchoring of the pressure line, which is the subject of the present paper. Thermal anchoring is applied to deviate heat flux to the cryogenic bath. This influence is much greater than was estimated during the preparation of the International Temperature Scale of 1990. It is therefore strongly suggested, on the basis of the present calculations, that for those cases where the diameter of the pressure line exceeds 1 mm, the temperature for thermal anchoring of the pressure line should be well above 25 K to 30 K (or no anchoring should be applied at all) in order that both the non-uniqueness between realizations and the interpolation residuals are minimized, with 3 K and 5 K as the lower fixed points. Where this is not possible, the negative effects of thermal anchoring can be compensated, for any anchoring temperature, by reducing the diameter of the pressure line below the anchor point to 1 mm.