diff --git a/protob/messages.proto b/protob/messages.proto
index 601572099..4a3a14f75 100644
--- a/protob/messages.proto
+++ b/protob/messages.proto
@@ -722,6 +722,7 @@ message SetU2FCounter {
  * @next Failure
  */
 message FirmwareErase {
+	optional uint32 length = 1;			// length of new firmware
 }
 
 /**