diff --git a/message.go b/message.go
index 98561734..83f51e6f 100644
--- a/message.go
+++ b/message.go
@@ -218,8 +218,8 @@ func WriteMessageN(w io.Writer, msg Message, pver uint32, btcnet BitcoinNet) (in
 	// Encode the header for the message.  This is done to a buffer
 	// rather than directly to the writer since writeElements doesn't
 	// return the number of bytes written.
-	var hw bytes.Buffer
-	writeElements(&hw, hdr.magic, command, hdr.length, hdr.checksum)
+	hw := bytes.NewBuffer(make([]byte, 0, MessageHeaderSize))
+	writeElements(hw, hdr.magic, command, hdr.length, hdr.checksum)
 
 	// Write header.
 	n, err := w.Write(hw.Bytes())
diff --git a/msgtx.go b/msgtx.go
index f7cd87d0..61b77c99 100644
--- a/msgtx.go
+++ b/msgtx.go
@@ -157,9 +157,9 @@ func (msg *MsgTx) TxSha() (ShaHash, error) {
 	// cause a run-time panic.  Also, SetBytes can't fail here due to the
 	// fact DoubleSha256 always returns a []byte of the right size
 	// regardless of input.
-	var buf bytes.Buffer
+	buf := bytes.NewBuffer(make([]byte, 0, msg.SerializeSize()))
+	_ = msg.Serialize(buf)
 	var sha ShaHash
-	_ = msg.Serialize(&buf)
 	_ = sha.SetBytes(DoubleSha256(buf.Bytes()))
 
 	// Even though this function can't currently fail, it still returns