The present invention relates to a frequency-control unit (310) for use in controlling an external controllable reference- frequency source. The frequency-control unit comprises a filter unit (314) with a controllable filter parameter (k), which is configured to derive, using the filter parameter, from a frequency-error signal (FOE) a frequency-control signal (FOC) for minimizing the frequency error of the reference frequency; and a correlation unit (314.3), which is configured to determine from frequency errors (FOE) of the reference frequency at different points in time (n, n+1) a correlation measure indicative of a correlation between the frequency errors (FOE) at the different points in time. The frequency-control unit is configured to adapt the controllable filter parameter (k) of the filter unit in dependence on the determined correlation measure. In particular embodiments presented, the value of the filter parameter (k) depends also on a receiver path strength, such as a RSCP value.