A heat exchanger with improved leak prevention may include a first heat exchanger plate, a second heat exchanger plate, a gasket between the first and the second heat exchanger plates, and a lock strip configured to maintain alignment of the first and second heat exchanger plates over a plurality of thermal expansion and contraction cycles of the plates. The lock strip may include at least one projection to engage with a projection of the first and/or second heat exchanger plate to secure its position over the plurality of thermal expansion and contraction cycles of the plates. Lock strips can be applied to one or many plates comprising a plate heat exchanger plate pack.