'0' is a valid sequence number (it comes after '9'), so we have

to see if the sequence number is set, not just if it's true.

diff --git a/Sip.pm b/Sip.pm
index a42b270..36a0f53 100644 (file)
--- a/Sip.pm
+++ b/Sip.pm
@@ -140,7 +140,7 @@ sub write_msg {
     my $cksum;
 
     if ($error_detection) {
-       if ($self->{seqno}) {
+       if (defined($self->{seqno})) {
            $msg .= 'AY' . $self->{seqno};
        }
        $msg .= 'AZ';