The present invention introduces a heat exchanger including a stack of heat transfer plates positioned between two end plates in which recesses formed in edge regions are adapted to accommodate bolts reaching from a first to a second of said two end plates, said at least one of said recesses formed with locking features adapted to engage with a locking device including an opening, where the locking device is to be positioned on the respective end plate with the opening aligned with the recess in such a manner that a bolt positioned in the recess also can project through said opening. This prevents the bold from falling out of the recesses.