A positioning node (110), a user equipment (120), a radio network node (130) and methods therein for providing complementary assistance data to be used by a user equipment (120) during a positioning session for determining a position of the user equipment (120) and for enabling continuation of the positioning session are provided. A change from a first cell to a second cell occurs during the positioning session. The user equipment (120) receives control information from the first cell before the change and from the second cell after the change. The positioning node obtains information identifying the second cell. Next, the positioning node generates the complementary assistance data relating to the second cell in advance of the change. The complementary assistance data comprises assistance data adapted to the second cell when the second cell is configured to provide control information to the user equipment (120). The positioning node sends the complementary assistance data relating to the second cell to the user equipment (120) via the radio network node (130) in advance of the change. Next, the user equipment (120) processes the complementary assistance data, thereby enabling continuation of the positioning session.