The present invention relates to a locking arrangement for a cover structure of a portable terminal device of a telecommunication system. The cover structure comprises at least one frame part (14), a cover part (16) connected to the frame part that can be removed from the frame part by the user, and locking elements for attaching the cover part to the frame part. In order that one could achieve a secure attachment and locking for the accumulator cover or accumulator packet of the device that at the same time enables the eliminating of the excessive clearances between the can parts, the locking elements comprise, in the frame part and cover part, slide bars (50, 51) and slide grooves (80) corresponding to each other.