The disclosure relates to a method (200) performed in a cyclic redundancy check, CRC, device (300) for calculating, based on a generator polynomial G(x), a CRC code for a message block. The method (200) comprises receiving (201) n segments of the message block in forward order or in reverse order, wherein at least one segment is received in reverse order; calculating (202) for each of the n segments a respective segment CRC code based on the generator polynomial G(x), wherein each segment CRC is calculated according to the received order of the segment; aligning (203) each of the n segment CRC codes; and calculating (204) the CRC code for the message block by adding together each of the aligned n segment CRC codes. The disclosure also relates to a device (300), computer program and computer program product.