diff --git a/bitcoin/signature.c b/bitcoin/signature.c
index 8067566d4..6b796b930 100644
--- a/bitcoin/signature.c
+++ b/bitcoin/signature.c
@@ -93,7 +93,6 @@ static void sha256_tx_one_input(struct bitcoin_tx *tx,
 				const u8 *script, size_t script_len,
 				struct sha256_double *hash)
 {
-	struct sha256_ctx ctx = SHA256_INIT;
 	size_t i;
 
 	assert(input_num < tx->input_count);
@@ -105,11 +104,7 @@ static void sha256_tx_one_input(struct bitcoin_tx *tx,
 	tx->input[input_num].script_length = script_len;
 	tx->input[input_num].script = cast_const(u8 *, script);
 
-	sha256_init(&ctx);
-	sha256_tx_for_sig(&ctx, tx, input_num);
-	sha256_le32(&ctx, SIGHASH_ALL);
-
-	sha256_double_done(&ctx, hash);
+	sha256_tx_for_sig(hash, tx, input_num, SIGHASH_ALL);
 
 	/* Reset it for next time. */
 	tx->input[input_num].script_length = 0;
diff --git a/bitcoin/tx.c b/bitcoin/tx.c
index aa5ce2040..4b59c730c 100644
--- a/bitcoin/tx.c
+++ b/bitcoin/tx.c
@@ -171,17 +171,24 @@ static void add_sha(const void *data, size_t len, void *shactx_)
 	sha256_update(ctx, memcheck(data, len), len);
 }
 
-void sha256_tx_for_sig(struct sha256_ctx *ctx, const struct bitcoin_tx *tx,
-		       unsigned int input_num)
+void sha256_tx_for_sig(struct sha256_double *h, const struct bitcoin_tx *tx,
+		       unsigned int input_num, enum sighash_type stype)
 {
 	size_t i;
+	struct sha256_ctx ctx = SHA256_INIT;
+
+	/* We only support this. */
+	assert(stype == SIGHASH_ALL);
 
 	/* Caller should zero-out other scripts for signing! */
 	assert(input_num < tx->input_count);
 	for (i = 0; i < tx->input_count; i++)
 		if (i != input_num)
 			assert(tx->input[i].script_length == 0);
-	add_tx(tx, add_sha, ctx, false);
+	add_tx(tx, add_sha, &ctx, false);
+
+	sha256_le32(&ctx, stype);
+	sha256_double_done(&ctx, h);
 }
 
 static void add_linearize(const void *data, size_t len, void *pptr_)
diff --git a/bitcoin/tx.h b/bitcoin/tx.h
index 75afaf9b5..831c824be 100644
--- a/bitcoin/tx.h
+++ b/bitcoin/tx.h
@@ -2,6 +2,7 @@
 #define LIGHTNING_BITCOIN_TX_H
 #include "config.h"
 #include "shadouble.h"
+#include "signature.h"
 #include <ccan/short_types/short_types.h>
 #include <ccan/tal/tal.h>
 
@@ -43,8 +44,8 @@ struct bitcoin_tx_input {
 void bitcoin_txid(const struct bitcoin_tx *tx, struct sha256_double *txid);
 
 /* Useful for signature code. */
-void sha256_tx_for_sig(struct sha256_ctx *ctx, const struct bitcoin_tx *tx,
-		       unsigned int input_num);
+void sha256_tx_for_sig(struct sha256_double *h, const struct bitcoin_tx *tx,
+		       unsigned int input_num, enum sighash_type stype);
 
 /* Linear bytes of tx. */
 u8 *linearize_tx(const tal_t *ctx, const struct bitcoin_tx *tx);