diff --git a/common/hsm_version.h b/common/hsm_version.h
index 0b58011b3..8470dce64 100644
--- a/common/hsm_version.h
+++ b/common/hsm_version.h
@@ -15,6 +15,7 @@
  * v4 with sign_any_penalty_to_us: ead7963185194a515d1f14d2c44401392575299d68ce9a13d8a12baff3cf4f35
  * v4 with sign_anchorspend: 8a30722e38b56e82af566b9629ff18da01fcebd1e80ec67f04d8b3a2fa66d81c
  * v4 with sign_htlc_tx_mingle: b9247e75d41ee1b3fc2f7db0bac8f4e92d544ab2f017d430ae3a000589c384e5
+ * v4 with splicing: 06f21012936f825913af289fa81af1512c9ada1cb97c611698975a8fd287edbb
  */
 #define HSM_MIN_VERSION 3
 #define HSM_MAX_VERSION 4
diff --git a/hsmd/hsmd.c b/hsmd/hsmd.c
index f94040aec..73119731d 100644
--- a/hsmd/hsmd.c
+++ b/hsmd/hsmd.c
@@ -661,6 +661,7 @@ static struct io_plan *handle_client(struct io_conn *conn, struct client *c)
 	case WIRE_HSMD_SIGN_REMOTE_COMMITMENT_TX:
 	case WIRE_HSMD_SIGN_REMOTE_HTLC_TX:
 	case WIRE_HSMD_SIGN_MUTUAL_CLOSE_TX:
+	case WIRE_HSMD_SIGN_SPLICE_TX:
 	case WIRE_HSMD_GET_PER_COMMITMENT_POINT:
 	case WIRE_HSMD_SIGN_WITHDRAWAL:
 	case WIRE_HSMD_GET_CHANNEL_BASEPOINTS:
diff --git a/hsmd/hsmd_wire.csv b/hsmd/hsmd_wire.csv
index 2c7afecb9..66179b3c9 100644
--- a/hsmd/hsmd_wire.csv
+++ b/hsmd/hsmd_wire.csv
@@ -248,6 +248,12 @@ msgtype,hsmd_sign_mutual_close_tx,21
 msgdata,hsmd_sign_mutual_close_tx,tx,bitcoin_tx,
 msgdata,hsmd_sign_mutual_close_tx,remote_funding_key,pubkey,
 
+# channeld asks HSM to sign splice tx.
+msgtype,hsmd_sign_splice_tx,29
+msgdata,hsmd_sign_splice_tx,tx,bitcoin_tx,
+msgdata,hsmd_sign_splice_tx,remote_funding_key,pubkey,
+msgdata,hsmd_sign_splice_tx,input_index,u32,
+
 # Reply for all the above requests.
 msgtype,hsmd_sign_tx_reply,112
 msgdata,hsmd_sign_tx_reply,sig,bitcoin_signature,
diff --git a/hsmd/libhsmd.c b/hsmd/libhsmd.c
index 887136000..f0f02bee9 100644
--- a/hsmd/libhsmd.c
+++ b/hsmd/libhsmd.c
@@ -106,6 +106,9 @@ bool hsmd_check_client_capabilities(struct hsmd_client *client,
 	case WIRE_HSMD_SIGN_MUTUAL_CLOSE_TX:
 		return (client->capabilities & HSM_CAP_SIGN_CLOSING_TX) != 0;
 
+	case WIRE_HSMD_SIGN_SPLICE_TX:
+		return (client->capabilities & HSM_CAP_SIGN_CLOSING_TX) != 0;
+
 	case WIRE_HSMD_SIGN_OPTION_WILL_FUND_OFFER:
 		return (client->capabilities & HSM_CAP_SIGN_WILL_FUND_OFFER) != 0;
 
@@ -1162,6 +1165,40 @@ static u8 *handle_sign_mutual_close_tx(struct hsmd_client *c, const u8 *msg_in)
 	return towire_hsmd_sign_tx_reply(NULL, &sig);
 }
 
+/* This is used by channeld to sign the final splice tx. */
+static u8 *handle_sign_splice_tx(struct hsmd_client *c, const u8 *msg_in)
+{
+	struct secret channel_seed;
+	struct bitcoin_tx *tx;
+	struct pubkey remote_funding_pubkey, local_funding_pubkey;
+	struct bitcoin_signature sig;
+	struct secrets secrets;
+	unsigned int input_index;
+	const u8 *funding_wscript;
+
+	if (!fromwire_hsmd_sign_splice_tx(tmpctx, msg_in,
+					  &tx,
+					  &remote_funding_pubkey,
+					  &input_index))
+		return hsmd_status_malformed_request(c, msg_in);
+
+	tx->chainparams = c->chainparams;
+	get_channel_seed(&c->id, c->dbid, &channel_seed);
+	derive_basepoints(&channel_seed,
+			  &local_funding_pubkey, NULL, &secrets, NULL);
+
+	funding_wscript = bitcoin_redeem_2of2(tmpctx,
+					      &local_funding_pubkey,
+					      &remote_funding_pubkey);
+
+	sign_tx_input(tx, input_index, NULL, funding_wscript,
+		      &secrets.funding_privkey,
+		      &local_funding_pubkey,
+		      SIGHASH_ALL, &sig);
+
+	return towire_hsmd_sign_tx_reply(NULL, &sig);
+}
+
 /*~ Originally, onchaind would ask for hsmd to sign txs directly, and then
  * tell lightningd to broadcast it.  With "bring-your-own-fees" HTLCs, this
  * changed, since we need to find a UTXO to attach to the transaction,
@@ -1901,6 +1938,8 @@ u8 *hsmd_handle_client_message(const tal_t *ctx, struct hsmd_client *client,
 		return handle_sign_withdrawal_tx(client, msg);
 	case WIRE_HSMD_SIGN_MUTUAL_CLOSE_TX:
 		return handle_sign_mutual_close_tx(client, msg);
+	case WIRE_HSMD_SIGN_SPLICE_TX:
+		return handle_sign_splice_tx(client, msg);
 	case WIRE_HSMD_SIGN_LOCAL_HTLC_TX:
 		return handle_sign_local_htlc_tx(client, msg);
 	case WIRE_HSMD_SIGN_REMOTE_HTLC_TX: