It is presented a method, executed in a root sequence determiner for a base station controlling a first cell, the first cell being associated with at least one root sequence used for cell differentiation on a random access channel. The method comprises the steps of: obtaining information on root sequences of neighboring cells; when a root sequence conflict is found between the first cell and a neighboring cell, here denoted a conflict cell, determining if the conflict cell is of a higher priority than the first cell, the priorities of the first cell and the conflict cell being based on properties of the respective cells; and when the conflict cell is of a higher priority than the first cell, finding a new root sequence for the first cell, avoiding the root sequences of the neighboring cells.