The present invention relates to a method of updating the clock bias between the common clock of the satellites of a radio navigation satellite system and the clock of a radio station of an asynchronous cellular radiotelephone system including a mobile device including a radio navigation satellite system receiver for receiving satellite data supplied by at least four satellites and an assistance server for improving the acquisition of satellite data by the mobile device. The method includes the steps of the mobile device receiving the satellite data, the mobile device calculating pseudodistances between itself and the satellites, encapsulating the pseudodistances with the time at which the pseudodistances are calculated, transmitting the pseudodistances and the time at which the pseudodistances are calculated in the form of a radio signal from the mobile device to the assistance server via the radio station, and the assistance server determining the position of the mobile device and estimating the clock bias between the common clock of the satellites and the clock of the radio station using the pseudodistances and the time at which the pseudodistances are calculated.