diff --git a/common/psbt_open.c b/common/psbt_open.c
index c0a7b0f4a..c84bc7de6 100644
--- a/common/psbt_open.c
+++ b/common/psbt_open.c
@@ -324,7 +324,6 @@ u8 *psbt_changeset_get_next(const tal_t *ctx, struct channel_id *cid,
 
 	if (tal_count(set->added_ins) != 0) {
 		const struct input_set *in = &set->added_ins[0];
-		u16 max_witness_len;
 		u8 *script;
 
 		if (!psbt_get_serial_id(&in->input.unknowns, &serial_id))
@@ -333,10 +332,6 @@ u8 *psbt_changeset_get_next(const tal_t *ctx, struct channel_id *cid,
 		const u8 *prevtx = linearize_wtx(ctx,
 						 in->input.utxo);
 
-		if (!psbt_input_get_max_witness_len(&in->input,
-						    &max_witness_len))
-			abort();
-
 		if (in->input.redeem_script_len)
 			script = tal_dup_arr(ctx, u8,
 					     in->input.redeem_script,
@@ -347,7 +342,6 @@ u8 *psbt_changeset_get_next(const tal_t *ctx, struct channel_id *cid,
 		msg = towire_tx_add_input(ctx, cid, serial_id,
 					  prevtx, in->tx_input.index,
 					  in->tx_input.sequence,
-					  max_witness_len,
 					  script,
 					  NULL);
 
@@ -440,49 +434,15 @@ int psbt_find_serial_output(struct wally_psbt *psbt, u16 serial_id)
 	return -1;
 }
 
-void psbt_input_add_max_witness_len(struct wally_psbt_input *input,
-				    u16 max_witness_len)
-{
-	u8 *key = psbt_make_key(tmpctx, PSBT_TYPE_MAX_WITNESS_LEN, NULL);
-	beint16_t bev = cpu_to_be16(max_witness_len);
-
-	psbt_input_add_unknown(input, key, &bev, sizeof(bev));
-}
-
-
-bool psbt_input_get_max_witness_len(const struct wally_psbt_input *input,
-				    u16 *max_witness_len)
-{
-	size_t value_len;
-	beint16_t bev;
-	void *result = psbt_get_lightning(&input->unknowns,
-					  PSBT_TYPE_MAX_WITNESS_LEN,
-					  &value_len);
-	if (!result)
-		return false;
-
-	if (value_len != sizeof(bev))
-		return false;
-
-	memcpy(&bev, result, value_len);
-	*max_witness_len = be16_to_cpu(bev);
-	return true;
-}
-
 bool psbt_has_required_fields(struct wally_psbt *psbt)
 {
-	u16 max_witness, serial_id;
+	u16 serial_id;
 	for (size_t i = 0; i < psbt->num_inputs; i++) {
 		struct wally_psbt_input *input = &psbt->inputs[i];
 
 		if (!psbt_get_serial_id(&input->unknowns, &serial_id))
 			return false;
 
-		/* Inputs had also better have their max_witness_lens
-		 * filled in! */
-		if (!psbt_input_get_max_witness_len(input, &max_witness))
-			return false;
-
 		/* Required because we send the full tx over the wire now */
 		if (!input->utxo)
 			return false;
diff --git a/common/psbt_open.h b/common/psbt_open.h
index 50c1ee72f..7c1f96320 100644
--- a/common/psbt_open.h
+++ b/common/psbt_open.h
@@ -124,24 +124,6 @@ int psbt_find_serial_input(struct wally_psbt *psbt, u16 serial_id);
  */
 int psbt_find_serial_output(struct wally_psbt *psbt, u16 serial_id);
 
-/* psbt_input_add_max_witness_len - Put a max witness len on a thing
- *
- * @input - input to add max-witness-len to
- * @max_witness_len - value
- */
-void psbt_input_add_max_witness_len(struct wally_psbt_input *input,
-				    u16 max_witness_len);
-
-/* psbt_input_get_max_witness_len - Get the max_witness_len
- *
- * @input - psbt input to look for max witness len on
- * @max_witness_len - found length
- *
- * Returns false if key not present */
-WARN_UNUSED_RESULT bool
-psbt_input_get_max_witness_len(const struct wally_psbt_input *input,
-			       u16 *max_witness_len);
-
 /* psbt_has_required_fields - Validates psbt field completion
  *
  * Required fields are:
diff --git a/common/test/exp-run-psbt_diff.c b/common/test/exp-run-psbt_diff.c
index bd8402571..9d077c09a 100644
--- a/common/test/exp-run-psbt_diff.c
+++ b/common/test/exp-run-psbt_diff.c
@@ -56,7 +56,7 @@ void towire_secp256k1_ecdsa_signature(u8 **pptr UNNEEDED,
 void towire_sha256(u8 **pptr UNNEEDED, const struct sha256 *sha256 UNNEEDED)
 { fprintf(stderr, "towire_sha256 called!\n"); abort(); }
 /* Generated stub for towire_tx_add_input */
-u8 *towire_tx_add_input(const tal_t *ctx UNNEEDED, const struct channel_id *channel_id UNNEEDED, u16 serial_id UNNEEDED, const u8 *prevtx UNNEEDED, u32 prevtx_vout UNNEEDED, u32 sequence UNNEEDED, u16 max_witness_len UNNEEDED, const u8 *script UNNEEDED, const struct tlv_tx_add_input_tlvs *tlvs UNNEEDED)
+u8 *towire_tx_add_input(const tal_t *ctx UNNEEDED, const struct channel_id *channel_id UNNEEDED, u16 serial_id UNNEEDED, const u8 *prevtx UNNEEDED, u32 prevtx_vout UNNEEDED, u32 sequence UNNEEDED, const u8 *script UNNEEDED, const struct tlv_tx_add_input_tlvs *tlvs UNNEEDED)
 { fprintf(stderr, "towire_tx_add_input called!\n"); abort(); }
 /* Generated stub for towire_tx_add_output */
 u8 *towire_tx_add_output(const tal_t *ctx UNNEEDED, const struct channel_id *channel_id UNNEEDED, u16 serial_id UNNEEDED, u64 sats UNNEEDED, const u8 *script UNNEEDED)
@@ -180,8 +180,10 @@ int main(int argc, const char *argv[])
 	diff_count(end, start, 1, 1);
 
 	/* Add some extra unknown info to a PSBT */
-	psbt_input_add_max_witness_len(&end->inputs[1], 100);
-	psbt_input_add_max_witness_len(&start->inputs[1], 100);
+	u8 *key = psbt_make_key(tmpctx, 0x05, NULL);
+	char *val = tal_fmt(tmpctx, "hello");
+	psbt_input_add_unknown(&end->inputs[1], key, val, tal_bytelen(val));
+	psbt_input_add_unknown(&start->inputs[1], key, val, tal_bytelen(val));
 
 	/* Swap locations */
 	struct wally_map_item tmp;
@@ -190,7 +192,6 @@ int main(int argc, const char *argv[])
 	end->inputs[1].unknowns.items[1] = tmp;
 
 	/* We expect nothing to change ? */
-	/* FIXME: stable ordering of unknowns ? */
 	diff_count(start, end, 1, 1);
 	diff_count(end, start, 1, 1);
 
diff --git a/openingd/dualopend.c b/openingd/dualopend.c
index 2b11394b2..e563db2d6 100644
--- a/openingd/dualopend.c
+++ b/openingd/dualopend.c
@@ -239,14 +239,6 @@ static size_t psbt_input_weight(struct wally_psbt *psbt,
 				size_t in)
 {
 	size_t weight;
-	u16 max_witness_len;
-	bool ok;
-
-	/* BOLT-fe0351ca2cea3105c4f2eb18c571afca9d21c85b #2
-	 * `max_witness_len` is the total serialized length of the
-	 * witness data that will be supplied (e.g. sizeof(varint) +
-	 * sizeof(witness) for each) in `funding_signed2`.
-	 */
 
 	/* txid + txout + sequence */
 	weight = (32 + 4 + 4) * 4;
@@ -254,10 +246,10 @@ static size_t psbt_input_weight(struct wally_psbt *psbt,
 		(psbt->inputs[in].redeem_script_len +
 			(varint_t) varint_size(psbt->inputs[in].redeem_script_len)) * 4;
 
-	ok = psbt_input_get_max_witness_len(&psbt->inputs[in],
-					    &max_witness_len);
-	assert(ok);
-	weight += max_witness_len;
+	/* BOLT-78de9a79b491ae9fb84b1fdb4546bacf642dce87 #2
+	 * The minimum witness weight for an input is 110.
+	 */
+	weight += 110;
 	return weight;
 }
 
@@ -590,7 +582,6 @@ static bool run_tx_interactive(struct state *state, struct wally_psbt **orig_psb
 		switch (t) {
 		case WIRE_TX_ADD_INPUT: {
 			const u8 *tx_bytes, *redeemscript;
-			u16 max_witness_len;
 			u32 outnum, sequence;
 			size_t len;
 			struct bitcoin_tx *tx;
@@ -603,7 +594,6 @@ static bool run_tx_interactive(struct state *state, struct wally_psbt **orig_psb
 						   &serial_id,
 						   cast_const2(u8 **, &tx_bytes),
 						   &outnum, &sequence,
-						   &max_witness_len,
 						   cast_const2(u8 **, &redeemscript),
 						   add_tlvs))
 				peer_failed(state->pps, &state->channel_id,
@@ -697,7 +687,6 @@ static bool run_tx_interactive(struct state *state, struct wally_psbt **orig_psb
 			}
 
 			psbt_input_add_serial_id(in, serial_id);
-			psbt_input_add_max_witness_len(in, max_witness_len);
 
 			/* FIXME: what's in the tlv? */
 			break;
diff --git a/wire/extracted_peer_experimental_dual_fund b/wire/extracted_peer_experimental_dual_fund
index 600ed1421..12c7aa1b5 100644
--- a/wire/extracted_peer_experimental_dual_fund
+++ b/wire/extracted_peer_experimental_dual_fund
@@ -1,6 +1,6 @@
 --- wire/extracted_peer_wire_csv	2020-07-28 12:36:12.063168014 -0500
-+++ -	2020-08-24 19:16:50.026185750 -0500
-@@ -31,6 +31,47 @@
++++ -	2020-08-31 21:00:40.856646471 -0500
+@@ -31,6 +31,46 @@
  tlvdata,n2,tlv1,amount_msat,tu64,
  tlvtype,n2,tlv2,11
  tlvdata,n2,tlv2,cltv_expiry,tu32,
@@ -11,7 +11,6 @@
 +msgdata,tx_add_input,prevtx,byte,prevtx_len
 +msgdata,tx_add_input,prevtx_vout,u32,
 +msgdata,tx_add_input,sequence,u32,
-+msgdata,tx_add_input,max_witness_len,u16,
 +msgdata,tx_add_input,redeemscript_len,u16,
 +msgdata,tx_add_input,script,byte,redeemscript_len
 +msgdata,tx_add_input,tlvs,tx_add_input_tlvs,
@@ -48,7 +47,7 @@
  msgtype,open_channel,32
  msgdata,open_channel,chain_hash,chain_hash,
  msgdata,open_channel,temporary_channel_id,byte,32
-@@ -82,6 +123,54 @@
+@@ -82,6 +122,54 @@
  msgtype,funding_locked,36
  msgdata,funding_locked,channel_id,channel_id,
  msgdata,funding_locked,next_per_commitment_point,point,
@@ -103,7 +102,7 @@
  msgtype,shutdown,38
  msgdata,shutdown,channel_id,channel_id,
  msgdata,shutdown,len,u16,
-@@ -169,6 +258,11 @@
+@@ -169,6 +257,11 @@
  msgdata,channel_update,fee_base_msat,u32,
  msgdata,channel_update,fee_proportional_millionths,u32,
  msgdata,channel_update,htlc_maximum_msat,u64,,option_channel_htlc_max