diff --git a/firmware/signing.c b/firmware/signing.c
index 05cb9054b3..2aff6bd21c 100644
--- a/firmware/signing.c
+++ b/firmware/signing.c
@@ -478,9 +478,13 @@ void signing_init(const SignTx *msg, const CoinInfo *_coin, const HDNode *_root)
 	version = msg->version;
 	lock_time = msg->lock_time;
 
-	tx_weight = 4 * (TXSIZE_HEADER + TXSIZE_FOOTER
-					 + ser_length_size(inputs_count)
-					 + ser_length_size(outputs_count));
+	uint32_t size = TXSIZE_HEADER + TXSIZE_FOOTER + ser_length_size(inputs_count) + ser_length_size(outputs_count);
+	if (coin->decred) {
+		size += 4; // Decred expiry
+		size += ser_length_size(inputs_count); // Witness inputs count
+	}
+
+	tx_weight = 4 * size;
 
 	signatures = 0;
 	idx1 = 0;
@@ -904,7 +908,12 @@ void signing_txack(TransactionType *tx)
 	switch (signing_stage) {
 		case STAGE_REQUEST_1_INPUT:
 			signing_check_input(&tx->inputs[0]);
-			tx_weight += tx_input_weight(&tx->inputs[0]);
+
+			tx_weight += tx_input_weight(coin, &tx->inputs[0]);
+			if (coin->decred) {
+				tx_weight += tx_decred_witness_weight(&tx->inputs[0]);
+			}
+
 			if (tx->inputs[0].script_type == InputScriptType_SPENDMULTISIG
 				|| tx->inputs[0].script_type == InputScriptType_SPENDADDRESS) {
 				memcpy(&input, tx->inputs, sizeof(TxInputType));
diff --git a/firmware/transaction.c b/firmware/transaction.c
index 7f46e61ea1..e99dc75786 100644
--- a/firmware/transaction.c
+++ b/firmware/transaction.c
@@ -53,6 +53,8 @@
 #define TXSIZE_P2PKHASH 25
 /* size of a p2sh script (hash, push, 20 scripthash, equal) */
 #define TXSIZE_P2SCRIPT 23
+/* size of a Decred witness (without script): 8 amount, 4 block height, 4 block index */
+#define TXSIZE_DECRED_WITNESS 16
 
 static const uint8_t segwit_header[2] = {0,1};
 
@@ -677,7 +679,7 @@ void tx_hash_final(TxStruct *t, uint8_t *hash, bool reverse)
 	}
 }
 
-uint32_t tx_input_weight(const TxInputType *txinput) {
+static uint32_t tx_input_script_size(const TxInputType *txinput) {
 	uint32_t input_script_size;
 	if (txinput->has_multisig) {
 		uint32_t multisig_script_size = TXSIZE_MULTISIGSCRIPT
@@ -688,6 +690,16 @@ uint32_t tx_input_weight(const TxInputType *txinput) {
 	} else {
 		input_script_size = (1 + TXSIZE_SIGNATURE + 1 + TXSIZE_PUBKEY);
 	}
+
+	return input_script_size;
+}
+
+uint32_t tx_input_weight(const CoinInfo *coin, const TxInputType *txinput) {
+	if (coin->decred) {
+		return 4 * (TXSIZE_INPUT + 1); // Decred tree
+	}
+
+	uint32_t input_script_size = tx_input_script_size(txinput);
 	uint32_t weight = 4 * TXSIZE_INPUT;
 	if (txinput->script_type == InputScriptType_SPENDADDRESS
 		|| txinput->script_type == InputScriptType_SPENDMULTISIG) {
@@ -740,5 +752,18 @@ uint32_t tx_output_weight(const CoinInfo *coin, const TxOutputType *txoutput) {
 		} 
 	}
 	output_script_size += ser_length_size(output_script_size);
-	return 4 * (TXSIZE_OUTPUT + output_script_size);
+
+	uint32_t size = TXSIZE_OUTPUT;
+	if (coin->decred) {
+		size += 2; // Decred script version
+	}
+
+	return 4 * (size + output_script_size);
+}
+
+uint32_t tx_decred_witness_weight(const TxInputType *txinput) {
+	uint32_t input_script_size = tx_input_script_size(txinput);
+	uint32_t size = TXSIZE_DECRED_WITNESS + ser_length_size(input_script_size) + input_script_size;
+
+	return 4 * size;
 }
diff --git a/firmware/transaction.h b/firmware/transaction.h
index 3695cfc4cc..cd344093ff 100644
--- a/firmware/transaction.h
+++ b/firmware/transaction.h
@@ -76,7 +76,8 @@ uint32_t tx_serialize_extra_data_hash(TxStruct *tx, const uint8_t *data, uint32_
 uint32_t tx_serialize_decred_witness_hash(TxStruct *tx, const TxInputType *input);
 void tx_hash_final(TxStruct *t, uint8_t *hash, bool reverse);
 
-uint32_t tx_input_weight(const TxInputType *txinput);
+uint32_t tx_input_weight(const CoinInfo *coin, const TxInputType *txinput);
 uint32_t tx_output_weight(const CoinInfo *coin, const TxOutputType *txoutput);
+uint32_t tx_decred_witness_weight(const TxInputType *txinput);
 
 #endif