Abstract: The invention relates to a locking member for the sides of commercial vehicles with a locking lever positioned in a hollow profile, in particular in a stanchion and which is pivotable with a locking hook and an articulation shaft about a pivoting axis. The locking hook engages in the locking position in an abutment of a side and can be pivoted with the aid of a control member engaging in the vicinity of the articulation shaft into an open position. In order to ensure a reliable locking and simultaneously a safe flapping down of a side subject to an internal pressure, the hollow profile and the articulation shaft of the locking hook are provided with engagement members constructed in complementary manner and which in the case of an internal pressure applied to the side pass from a pivoting position into an engagement position and block the opening movement of the locking lever.