In packet communications that employ header compression/decompression, the computational complexity of checksum generation can be reduced by re-using static checksum information associated with header bits (S) that do not change from header to header. The static checksum information can be used together with information about header bits (T) that do change from header to header, in order to generate a desired checksum (CS). The checksum can then be used to verify a reconstructed header (17) produced from a compressed header by a header decompressor.