smoltcp: Stuck at retransmitting

This code here https://github.com/m-labs/smoltcp/blob/master/src/socket/tcp.rs#L913 should either reset local_rx_dup_acks or let it count from 255 to 0 with a overflowing add or stay at 255 with a saturation. What is the desired behavior?

                        self.local_rx_dup_acks += 1;
                        if self.local_rx_dup_acks == 3 {
                        }

thread 'main' panicked at 'attempt to add with overflow', smoltcp/src/socket/tcp.rs:913:25