diff --git a/pkt.c b/pkt.c
index 16626a039..cb49f75dc 100644
--- a/pkt.c
+++ b/pkt.c
@@ -8,6 +8,11 @@
 #include "pkt.h"
 #include "protobuf_convert.h"
 
+size_t pkt_totlen(const struct pkt *pkt)
+{
+	return sizeof(pkt->len) + le32_to_cpu(pkt->len);
+}
+
 static struct pkt *to_pkt(const tal_t *ctx, Pkt__PktCase type, void *msg)
 {
 	struct pkt *ret;
diff --git a/pkt.h b/pkt.h
index 3e6d4735e..c8ff0fa48 100644
--- a/pkt.h
+++ b/pkt.h
@@ -20,6 +20,9 @@ struct pkt {
 Pkt *pkt_from_file(const char *filename, Pkt__PktCase expect);
 Pkt *any_pkt_from_file(const char *filename);
 
+/* Total length of packet, including header. */
+size_t pkt_totlen(const struct pkt *pkt);
+
 struct sha256;
 struct bitcoin_compressed_pubkey;
 struct signature;
diff --git a/test-cli/close-channel.c b/test-cli/close-channel.c
index 93cead442..789d10f6d 100644
--- a/test-cli/close-channel.c
+++ b/test-cli/close-channel.c
@@ -98,8 +98,7 @@ int main(int argc, char *argv[])
 		pkt = close_channel_complete_pkt(ctx, &sig);
 	else
 		pkt = close_channel_pkt(ctx, &sig);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/leak-anchor-sigs.c b/test-cli/leak-anchor-sigs.c
index 82dab6bac..b451bfa57 100644
--- a/test-cli/leak-anchor-sigs.c
+++ b/test-cli/leak-anchor-sigs.c
@@ -28,8 +28,7 @@ int main(int argc, char *argv[])
 		->open_anchor_scriptsigs;
 
 	pkt = leak_anchor_sigs_and_pretend_we_didnt_pkt(ctx, s);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/open-anchor-scriptsigs.c b/test-cli/open-anchor-scriptsigs.c
index d5677e376..fae59f6a2 100644
--- a/test-cli/open-anchor-scriptsigs.c
+++ b/test-cli/open-anchor-scriptsigs.c
@@ -95,8 +95,7 @@ int main(int argc, char *argv[])
 	}
 
 	pkt = open_anchor_sig_pkt(ctx, sigs, o1->anchor->n_inputs);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/open-channel.c b/test-cli/open-channel.c
index c99f2f5e4..d8ddde7c9 100644
--- a/test-cli/open-channel.c
+++ b/test-cli/open-channel.c
@@ -174,8 +174,7 @@ int main(int argc, char *argv[])
 	pkt = openchannel_pkt(ctx, weak_random64(), &revocation_hash, &outkey,
 			      commit_tx_fee, locktime_seconds, &anchor);
 
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/open-commit-sig.c b/test-cli/open-commit-sig.c
index 16ab9785e..18ebf400a 100644
--- a/test-cli/open-commit-sig.c
+++ b/test-cli/open-commit-sig.c
@@ -88,8 +88,7 @@ int main(int argc, char *argv[])
 		      privkey, &pubkey1, &sig);
 
 	pkt = open_commit_sig_pkt(ctx, &sig);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/update-channel-accept.c b/test-cli/update-channel-accept.c
index 6a16880c6..7e8f5c58d 100644
--- a/test-cli/update-channel-accept.c
+++ b/test-cli/update-channel-accept.c
@@ -106,8 +106,7 @@ int main(int argc, char *argv[])
 		      privkey, &pubkey1, &sig.sig);
 
 	pkt = update_accept_pkt(ctx, &sig.sig, &revocation_hash);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/update-channel-complete.c b/test-cli/update-channel-complete.c
index 93f968a75..6aad4282c 100644
--- a/test-cli/update-channel-complete.c
+++ b/test-cli/update-channel-complete.c
@@ -121,8 +121,7 @@ int main(int argc, char *argv[])
 	/* Hand over our preimage for previous tx. */
 	shachain_from_seed(&seed, num_updates, &preimage);
 	pkt = update_complete_pkt(ctx, &preimage);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/update-channel-signature.c b/test-cli/update-channel-signature.c
index c06d28e9f..3c8d8de26 100644
--- a/test-cli/update-channel-signature.c
+++ b/test-cli/update-channel-signature.c
@@ -124,8 +124,7 @@ int main(int argc, char *argv[])
 		      privkey, &pubkey1, &sig.sig);
 
 	pkt = update_signature_pkt(ctx, &sig.sig, &preimage);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);
diff --git a/test-cli/update-channel.c b/test-cli/update-channel.c
index 62eeb829e..1952857c6 100644
--- a/test-cli/update-channel.c
+++ b/test-cli/update-channel.c
@@ -63,8 +63,7 @@ int main(int argc, char *argv[])
 	       revocation_hash.u.u8, sizeof(revocation_hash.u.u8));
 	
 	pkt = update_pkt(ctx, &revocation_hash, this_delta);
-	if (!write_all(STDOUT_FILENO, pkt,
-		       sizeof(pkt->len) + le32_to_cpu(pkt->len)))
+	if (!write_all(STDOUT_FILENO, pkt, pkt_totlen(pkt)))
 		err(1, "Writing out packet");
 
 	tal_free(ctx);