diff --git a/src/algo_dup2.c b/src/algo_dup2.c
index b578749..6045c8d 100644
--- a/src/algo_dup2.c
+++ b/src/algo_dup2.c
@@ -82,11 +82,11 @@ int algo_dup2_on_datagram(struct evt_core_ctx* ctx, struct evt_core_fdinfo* fdin
   dup2c->emit_id = dup2c->emit_id + 1;
   union abstract_packet metadata = {
     .fmt.headers.cmd = CMD_UDP_METADATA_THUNDER,
-    .fmt.headers.size = sizeof(metadata.fmt.headers) + sizeof(metadata.fmt.content.udp_metadata_thunder),
+    .fmt.headers.size = sizeof(metadata),
     .fmt.headers.flags = 0,
     .fmt.content.udp_metadata_thunder.id = dup2c->emit_id
   };
-  buffer_append_ap (bp, &metadata);
+  union abstract_packet *apbuf = buffer_append_ap (bp, &metadata);
   if (ctx->verbose > 1) {
     dump_buffer_packet(bp);
     fprintf(stderr, "    [algo_dup2] Added metadata\n");