diff --git a/conn.go b/conn.go
index 9d3005b..a408e76 100644
--- a/conn.go
+++ b/conn.go
@@ -1242,7 +1242,7 @@ func (c *Conn) unmarshalHandshakeMessage(data []byte, transcript transcriptHash)
 	data = append([]byte(nil), data...)
 
 	if !m.unmarshal(data) {
-		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		return nil, c.in.setErrorLocked(c.sendAlert(alertDecodeError))
 	}
 
 	if transcript != nil {