diff --git a/firmware/protob/types.pb.c b/firmware/protob/types.pb.c
index 66c417590..5e6e1298a 100644
--- a/firmware/protob/types.pb.c
+++ b/firmware/protob/types.pb.c
@@ -29,9 +29,10 @@ const pb_field_t CoinType_fields[5] = {
     PB_LAST_FIELD
 };
 
-const pb_field_t MultisigRedeemScriptType_fields[3] = {
+const pb_field_t MultisigRedeemScriptType_fields[4] = {
     PB_FIELD(  1, BYTES   , REPEATED, STATIC  , FIRST, MultisigRedeemScriptType, pubkeys, pubkeys, 0),
     PB_FIELD(  2, BYTES   , REPEATED, STATIC  , OTHER, MultisigRedeemScriptType, signatures, pubkeys, 0),
+    PB_FIELD(  3, UINT32  , OPTIONAL, STATIC  , OTHER, MultisigRedeemScriptType, m, signatures, 0),
     PB_LAST_FIELD
 };
 
diff --git a/firmware/protob/types.pb.h b/firmware/protob/types.pb.h
index 3b91af929..11df556d6 100644
--- a/firmware/protob/types.pb.h
+++ b/firmware/protob/types.pb.h
@@ -102,6 +102,8 @@ typedef struct _MultisigRedeemScriptType {
     MultisigRedeemScriptType_pubkeys_t pubkeys[5];
     pb_size_t signatures_count;
     MultisigRedeemScriptType_signatures_t signatures[4];
+    bool has_m;
+    uint32_t m;
 } MultisigRedeemScriptType;
 
 typedef PB_BYTES_ARRAY_T(520) TxOutputBinType_script_pubkey_t;
@@ -191,7 +193,7 @@ extern const InputScriptType TxInputType_script_type_default;
 /* Initializer values for message structs */
 #define HDNodeType_init_default                  {0, 0, 0, {0, {0}}, false, {0, {0}}, false, {0, {0}}}
 #define CoinType_init_default                    {false, "", false, "", false, 0, false, 0}
-#define MultisigRedeemScriptType_init_default    {0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}, 0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}}
+#define MultisigRedeemScriptType_init_default    {0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}, 0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}, false, 0}
 #define TxInputType_init_default                 {0, {0, 0, 0, 0, 0, 0, 0, 0}, {0, {0}}, 0, false, {0, {0}}, false, 4294967295u, false, InputScriptType_SPENDADDRESS, false, MultisigRedeemScriptType_init_default}
 #define TxOutputType_init_default                {false, "", 0, {0, 0, 0, 0, 0, 0, 0, 0}, 0, (OutputScriptType)0}
 #define TxOutputBinType_init_default             {0, {0, {0}}}
@@ -200,7 +202,7 @@ extern const InputScriptType TxInputType_script_type_default;
 #define TxRequestSerializedType_init_default     {false, 0, false, {0, {0}}, false, {0, {0}}}
 #define HDNodeType_init_zero                     {0, 0, 0, {0, {0}}, false, {0, {0}}, false, {0, {0}}}
 #define CoinType_init_zero                       {false, "", false, "", false, 0, false, 0}
-#define MultisigRedeemScriptType_init_zero       {0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}, 0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}}
+#define MultisigRedeemScriptType_init_zero       {0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}, 0, {{0, {0}}, {0, {0}}, {0, {0}}, {0, {0}}}, false, 0}
 #define TxInputType_init_zero                    {0, {0, 0, 0, 0, 0, 0, 0, 0}, {0, {0}}, 0, false, {0, {0}}, false, 0, false, (InputScriptType)0, false, MultisigRedeemScriptType_init_zero}
 #define TxOutputType_init_zero                   {false, "", 0, {0, 0, 0, 0, 0, 0, 0, 0}, 0, (OutputScriptType)0}
 #define TxOutputBinType_init_zero                {0, {0, {0}}}
@@ -221,6 +223,7 @@ extern const InputScriptType TxInputType_script_type_default;
 #define HDNodeType_public_key_tag                6
 #define MultisigRedeemScriptType_pubkeys_tag     1
 #define MultisigRedeemScriptType_signatures_tag  2
+#define MultisigRedeemScriptType_m_tag           3
 #define TxOutputBinType_amount_tag               1
 #define TxOutputBinType_script_pubkey_tag        2
 #define TxOutputType_address_tag                 1
@@ -254,7 +257,7 @@ extern const InputScriptType TxInputType_script_type_default;
 /* Struct field encoding specification for nanopb */
 extern const pb_field_t HDNodeType_fields[7];
 extern const pb_field_t CoinType_fields[5];
-extern const pb_field_t MultisigRedeemScriptType_fields[3];
+extern const pb_field_t MultisigRedeemScriptType_fields[4];
 extern const pb_field_t TxInputType_fields[8];
 extern const pb_field_t TxOutputType_fields[5];
 extern const pb_field_t TxOutputBinType_fields[3];
@@ -265,11 +268,11 @@ extern const pb_field_t TxRequestSerializedType_fields[4];
 /* Maximum encoded size of messages (where known) */
 #define HDNodeType_size                          121
 #define CoinType_size                            47
-#define MultisigRedeemScriptType_size            663
-#define TxInputType_size                         1289
+#define MultisigRedeemScriptType_size            669
+#define TxInputType_size                         1295
 #define TxOutputType_size                        102
 #define TxOutputBinType_size                     534
-#define TransactionType_size                     1957
+#define TransactionType_size                     1963
 #define TxRequestDetailsType_size                40
 #define TxRequestSerializedType_size             1115
 
diff --git a/firmware/signing.c b/firmware/signing.c
index 4c21cc4b3..4193e96b9 100644
--- a/firmware/signing.c
+++ b/firmware/signing.c
@@ -282,8 +282,12 @@ void signing_txack(TransactionType *tx)
 				for (k = 0; k < tx->inputs[0].address_n_count; k++) {
 					hdnode_private_ckd(&node, tx->inputs[0].address_n[k]);
 				}
-				ecdsa_get_pubkeyhash(node.public_key, hash);
-				tx->inputs[0].script_sig.size = compile_script_sig(coin->address_type, hash, tx->inputs[0].script_sig.bytes);
+				if (tx->inputs[0].has_multisig) {
+					tx->inputs[0].script_sig.size = compile_script_multisig(&(tx->inputs[0].multisig), tx->inputs[0].script_sig.bytes);
+				} else {
+					ecdsa_get_pubkeyhash(node.public_key, hash);
+					tx->inputs[0].script_sig.size = compile_script_sig(coin->address_type, hash, tx->inputs[0].script_sig.bytes);
+				}
 				if (tx->inputs[0].script_sig.size == 0) {
 					fsm_sendFailure(FailureType_Failure_Other, "Failed to compile input");
 					signing_abort();
@@ -362,7 +366,26 @@ void signing_txack(TransactionType *tx)
 				resp.serialized.has_serialized_tx = true;
 				ecdsa_sign_digest(privkey, hash, sig);
 				resp.serialized.signature.size = ecdsa_sig_to_der(sig, resp.serialized.signature.bytes);
-				input.script_sig.size = serialize_script_sig(resp.serialized.signature.bytes, resp.serialized.signature.size, pubkey, 33, input.script_sig.bytes);
+				if (input.has_multisig) {
+					// fill in the signature
+					int i, pubkey_idx = -1;
+					for (i = 0; i < input.multisig.pubkeys_count; i++) {
+						if (input.multisig.pubkeys[i].size == 33 && memcmp(input.multisig.pubkeys[i].bytes, pubkey, 33) == 0) {
+							pubkey_idx = i;
+							break;
+						}
+					}
+					if (pubkey_idx == -1) {
+						fsm_sendFailure(FailureType_Failure_Other, "Pubkey not found in multisig script");
+						signing_abort();
+						return;
+					}
+					memcpy(input.multisig.signatures[pubkey_idx].bytes, resp.serialized.signature.bytes, resp.serialized.signature.size);
+					input.multisig.signatures[pubkey_idx].size = resp.serialized.signature.size;
+					input.script_sig.size = serialize_script_multisig(&(input.multisig), input.script_sig.bytes);
+				} else {
+					input.script_sig.size = serialize_script_sig(resp.serialized.signature.bytes, resp.serialized.signature.size, pubkey, 33, input.script_sig.bytes);
+				}
 				resp.serialized.serialized_tx.size = tx_serialize_input(&to, input.prev_hash.bytes, input.prev_index, input.script_sig.bytes, input.script_sig.size, input.sequence, resp.serialized.serialized_tx.bytes);
 				if (idx1i < inputs_count - 1) {
 					idx1i++;
diff --git a/firmware/transaction.c b/firmware/transaction.c
index fc3d6e144..958e740f1 100644
--- a/firmware/transaction.c
+++ b/firmware/transaction.c
@@ -130,7 +130,37 @@ uint32_t compile_script_sig(uint8_t address_type, const uint8_t *pubkeyhash, uin
 	}
 }
 
-int serialize_script_sig(uint8_t *signature, uint32_t signature_len, uint8_t *pubkey, uint32_t pubkey_len, uint8_t *out)
+// if out == NULL just compute the length
+uint32_t compile_script_multisig(const MultisigRedeemScriptType *multisig, uint8_t *out)
+{
+	if (!multisig->has_m) return 0;
+	uint32_t m = multisig->m;
+	uint32_t n = multisig->pubkeys_count;
+	if (m < 2 || m > 3) return 0;
+	if (n < 2 || n > 3) return 0;
+	uint32_t i, r = 0;
+	if (out) {
+		out[r] = 0x50 + m; r++;
+		for (i = 0; i < n; i++) {
+			r += op_push(multisig->pubkeys[i].size, out + r);
+			memcpy(out + r, multisig->pubkeys[i].bytes, multisig->pubkeys[i].size); r += multisig->pubkeys[i].size;
+		}
+		out[r] = 0x50 + n; r++;
+		out[r] = 0xAE; r++; // OP_CHECKMULTISIG
+	} else {
+		r++;
+		for (i = 0; i < n; i++) {
+			uint8_t dummy[8];
+			r += op_push(multisig->pubkeys[i].size, dummy);
+			r += multisig->pubkeys[i].size;
+		}
+		r++;
+		r++;
+	}
+	return r;
+}
+
+uint32_t serialize_script_sig(const uint8_t *signature, uint32_t signature_len, const uint8_t *pubkey, uint32_t pubkey_len, uint8_t *out)
 {
 	uint32_t r = 0;
 	r += op_push(signature_len + 1, out + r);
@@ -141,6 +171,24 @@ int serialize_script_sig(uint8_t *signature, uint32_t signature_len, uint8_t *pu
 	return r;
 }
 
+uint32_t serialize_script_multisig(const MultisigRedeemScriptType *multisig, uint8_t *out)
+{
+	uint32_t i, r = 0;
+	out[r] = 0x00; r++;
+	for (i = 0; i < multisig->signatures_count; i++) {
+		if (multisig->signatures[i].size == 0) {
+			continue;
+		}
+		r += op_push(multisig->signatures[i].size + 1, out + r);
+		memcpy(out + r, multisig->signatures[i].bytes, multisig->signatures[i].size); r += multisig->signatures[i].size;
+		out[r] = 0x01; r++;
+	}
+	uint32_t script_len = compile_script_multisig(multisig, 0);
+	r += op_push(script_len, out + r);
+	r += compile_script_multisig(multisig, out + r);
+	return r;
+}
+
 // tx methods
 
 uint32_t tx_serialize_header(TxStruct *tx, uint8_t *out)
diff --git a/firmware/transaction.h b/firmware/transaction.h
index 2a2e09849..eca3c16fa 100644
--- a/firmware/transaction.h
+++ b/firmware/transaction.h
@@ -42,7 +42,9 @@ typedef struct {
 } TxStruct;
 
 uint32_t compile_script_sig(uint8_t address_type, const uint8_t *pubkeyhash, uint8_t *out);
-int serialize_script_sig(uint8_t *signature, uint32_t signature_len, uint8_t *pubkey, uint32_t pubkey_len, uint8_t *out);
+uint32_t compile_script_multisig(const MultisigRedeemScriptType *multisig, uint8_t *out);
+uint32_t serialize_script_sig(const uint8_t *signature, uint32_t signature_len, const uint8_t *pubkey, uint32_t pubkey_len, uint8_t *out);
+uint32_t serialize_script_multisig(const MultisigRedeemScriptType *multisig, uint8_t *out);
 int compile_output(const CoinType *coin, const HDNode *root, TxOutputType *in, TxOutputBinType *out, bool needs_confirm);
 uint32_t tx_serialize_input(TxStruct *tx, uint8_t *prev_hash, uint32_t prev_index, uint8_t *script_sig, uint32_t script_sig_len, uint32_t sequence, uint8_t *out);
 uint32_t tx_serialize_output(TxStruct *tx, uint64_t amount, uint8_t *script_pubkey, uint32_t script_pubkey_len, uint8_t *out);
diff --git a/trezor-common b/trezor-common
index e675d5fd7..3670728fd 160000
--- a/trezor-common
+++ b/trezor-common
@@ -1 +1 @@
-Subproject commit e675d5fd7684e437bb35fb24330234d43ee2e4db
+Subproject commit 3670728fd205ccfc75571ec3a49bfc7d07d11b17