diff --git a/bitcoin/tx.c b/bitcoin/tx.c
index d1a7aea48..b460f8525 100644
--- a/bitcoin/tx.c
+++ b/bitcoin/tx.c
@@ -293,32 +293,6 @@ static bool uses_witness(const struct bitcoin_tx *tx)
 	return false;
 }
 
-/* BIP 141: The witness is a serialization of all witness data of the
- * transaction. Each txin is associated with a witness field. A
- * witness field starts with a var_int to indicate the number of stack
- * items for the txin.  */
-static void push_witnesses(const struct bitcoin_tx *tx,
-			  void (*push)(const void *, size_t, void *), void *pushp)
-{
-	for (size_t i = 0; i < tx->wtx->num_inputs; i++) {
-		struct wally_tx_witness_stack *witness = tx->wtx->inputs[i].witness;
-
-		/* Not every input needs a witness. */
-		if (!witness) {
-			push_varint(0, push, pushp);
-			continue;
-		}
-
-		push_varint(witness->num_items, push, pushp);
-		for (size_t j = 0; j < witness->num_items; j++) {
-			size_t witlen = witness->items[j].witness_len;
-			const u8 *wit = witness->items[j].witness;
-			push_varint(witlen, push, pushp);
-			push(wit, witlen, pushp);
-		}
-	}
-}
-
 /* For signing, we ignore input scripts on other inputs, and pretend
  * the current input has a certain script: this is indicated by a
  * non-NULL override_script.
@@ -377,23 +351,12 @@ u8 *linearize_tx(const tal_t *ctx, const struct bitcoin_tx *tx)
 	return arr;
 }
 
-static void push_measure(const void *data UNUSED, size_t len, void *lenp)
-{
-	*(size_t *)lenp += len;
-}
-
-size_t measure_tx_weight(const struct bitcoin_tx *tx)
+size_t bitcoin_tx_weight(const struct bitcoin_tx *tx)
 {
-	size_t non_witness_len = 0, witness_len = 0;
-	push_tx(tx, NULL, 0, push_measure, &non_witness_len, false);
-	if (uses_witness(tx)) {
-		push_witnesses(tx, push_measure, &witness_len);
-		/* Include BIP 144 marker and flag bytes in witness length */
-		witness_len += 2;
-	}
-
-	/* Normal bytes weigh 4 times more than Witness bytes */
-	return non_witness_len * 4 + witness_len;
+	size_t weight;
+	int ret = wally_tx_get_weight(tx->wtx, &weight);
+	assert(ret == WALLY_OK);
+	return weight;
 }
 
 void bitcoin_txid(const struct bitcoin_tx *tx, struct bitcoin_txid *txid)
diff --git a/bitcoin/tx.h b/bitcoin/tx.h
index 030be9d3e..3efb7b535 100644
--- a/bitcoin/tx.h
+++ b/bitcoin/tx.h
@@ -51,7 +51,7 @@ void bitcoin_txid(const struct bitcoin_tx *tx, struct bitcoin_txid *txid);
 u8 *linearize_tx(const tal_t *ctx, const struct bitcoin_tx *tx);
 
 /* Get weight of tx in Sipa. */
-size_t measure_tx_weight(const struct bitcoin_tx *tx);
+size_t bitcoin_tx_weight(const struct bitcoin_tx *tx);
 
 /* Allocate a tx: you just need to fill in inputs and outputs (they're
  * zeroed with inputs' sequence_number set to FFFFFFFF) */
diff --git a/lightningd/closing_control.c b/lightningd/closing_control.c
index eeac5ec24..8cd537190 100644
--- a/lightningd/closing_control.c
+++ b/lightningd/closing_control.c
@@ -64,7 +64,7 @@ static bool better_closing_fee(struct lightningd *ld,
 		  type_to_string(tmpctx, struct amount_sat, &last_fee));
 
 	/* Weight once we add in sigs. */
-	weight = measure_tx_weight(tx) + 74 * 2;
+	weight = bitcoin_tx_weight(tx) + 74 * 2;
 
 	/* If we don't have a feerate estimate, this gives feerate_floor */
 	min_feerate = feerate_min(ld, &feerate_unknown);
diff --git a/lightningd/onchain_control.c b/lightningd/onchain_control.c
index 8c38eb992..714a781d1 100644
--- a/lightningd/onchain_control.c
+++ b/lightningd/onchain_control.c
@@ -504,7 +504,7 @@ enum watch_result onchaind_funding_spent(struct channel *channel,
 				return KEEP_WATCHING;
 			}
 
-		feerate = fee.satoshis / measure_tx_weight(tx); /* Raw: reverse feerate extraction */
+		feerate = fee.satoshis / bitcoin_tx_weight(tx); /* Raw: reverse feerate extraction */
 		if (feerate < feerate_floor())
 			feerate = feerate_floor();
 	}
diff --git a/onchaind/onchaind.c b/onchaind/onchaind.c
index d8f95dbd1..74aefe45e 100644
--- a/onchaind/onchaind.c
+++ b/onchaind/onchaind.c
@@ -328,7 +328,7 @@ static struct bitcoin_tx *tx_to_us(const tal_t *ctx,
 	    tx, scriptpubkey_p2wpkh(tx, &our_wallet_pubkey), out->sat);
 
 	/* Worst-case sig is 73 bytes */
-	weight = measure_tx_weight(tx) + 1 + 3 + 73 + 0 + tal_count(wscript);
+	weight = bitcoin_tx_weight(tx) + 1 + 3 + 73 + 0 + tal_count(wscript);
 	fee = amount_tx_fee(feerate_per_kw, weight);
 
 	/* Result is trivial?  Spend with small feerate, but don't wait