In quantum field theory, sharp momentum states have to be normalized to be in Fock space. We investigate two different normalization schemes: box normalization and wave packets. These methods are equivalent in flat spacetimes, but turn out to produce different results in curved spacetimes, specifically in those that break translation invariance. This means that scattering processes have to be defined in relation to the normalization scheme used, rather than being independent of it as is the case in flat spacetime. We prove this and provide an illustrative example.