Handling of acknowledgement messages in terminal

The invention relates to handling of an acknowledgement message related to packet data transmission, said acknowledgement message acknowledging positively or negatively one or more data blocks sent from a terminal and said acknowledgement message comprising an information element related to the acknowledgement which element conditionally comprises a length field L, which indicates the length of the value part of said information element and possibly an uncompressed Ack/Nack bit map of varying length, which bit map length Lu may be calculated from the value of L with a predetermined calculation formula. In the method, one receives an acknowledgement message comprising said information element from a data transmission network and automatically ignores an uncompressed Ack/Nack bit map possibly included in the acknowledgement message, if said length field L is unspecified from the viewpoint of the terminal.