diff --git a/blockchain/fullblocktests/generate.go b/blockchain/fullblocktests/generate.go
index 4c551c05e0..963926e781 100644
--- a/blockchain/fullblocktests/generate.go
+++ b/blockchain/fullblocktests/generate.go
@@ -384,6 +384,8 @@ func additionalCoinbase(amount btcutil.Amount) func(*wire.MsgBlock) {
 		// Increase the first proof-of-work coinbase subsidy by the
 		// provided amount.
 		b.Transactions[0].TxOut[0].Value += int64(amount)
+
+		b.Transactions[0].WipeCache()
 	}
 }
 
@@ -402,6 +404,8 @@ func additionalSpendFee(fee btcutil.Amount) func(*wire.MsgBlock) {
 				fee))
 		}
 		b.Transactions[1].TxOut[0].Value -= int64(fee)
+
+		b.Transactions[1].WipeCache()
 	}
 }
 
@@ -410,6 +414,8 @@ func additionalSpendFee(fee btcutil.Amount) func(*wire.MsgBlock) {
 func replaceSpendScript(pkScript []byte) func(*wire.MsgBlock) {
 	return func(b *wire.MsgBlock) {
 		b.Transactions[1].TxOut[0].PkScript = pkScript
+
+		b.Transactions[1].WipeCache()
 	}
 }
 
@@ -418,6 +424,8 @@ func replaceSpendScript(pkScript []byte) func(*wire.MsgBlock) {
 func replaceCoinbaseSigScript(script []byte) func(*wire.MsgBlock) {
 	return func(b *wire.MsgBlock) {
 		b.Transactions[0].TxIn[0].SignatureScript = script
+
+		b.Transactions[0].WipeCache()
 	}
 }
 
diff --git a/wire/msgtx.go b/wire/msgtx.go
index 21e191d37f..58668b7eca 100644
--- a/wire/msgtx.go
+++ b/wire/msgtx.go
@@ -378,6 +378,13 @@ func (msg *MsgTx) TxHash() chainhash.Hash {
 	return chainhash.DoubleHashH(msg.cachedSeralizedNoWitness)
 }
 
+// WipeCache removes the cached serialized bytes of the transaction. This is
+// useful to be able to get the correct txid after mutating a transaction's
+// state.
+func (msg *MsgTx) WipeCache() {
+	msg.cachedSeralizedNoWitness = nil
+}
+
 // WitnessHash generates the hash of the transaction serialized according to
 // the new witness serialization defined in BIP0141 and BIP0144. The final
 // output is used within the Segregated Witness commitment of all the witnesses