backported from https://github.com/systemd/systemd/pull/16517/commits/6a47364968d4f1d1c515dddbfb0b9da18aac8709
--- a/src/libsystemd/sd-netlink/netlink-util.c
+++ b/src/libsystemd/sd-netlink/netlink-util.c
@@ -236,10 +236,10 @@
         if (r < 0)
                 return r;
 
+        rtnl_message_seal(*ret);
         (*ret)->hdr->nlmsg_seq = serial;
 
         err = NLMSG_DATA((*ret)->hdr);
-
         err->error = error;
 
         return 0;