diff --git a/update.cpp b/update.cpp
index e54b20c..f29c168 100644
--- a/update.cpp
+++ b/update.cpp
@@ -460,6 +460,13 @@ bool Update::downloadBinaryToDC(QString const &bFile) const {
                         //             10: OK
 
  10 :   bl_stopBL()     // leave bl and start (the new) application
+                        //
+                        // NOTE: this function MUST work under all conditions.
+                        // Alas, there is no direct result for this command, so
+                        // the only way of knowing it was successful is to ask
+                        // the device if the bootloader is still running.
+                        // There is no problem to repeat this command until the
+                        // bootloader is really not running anymore.
  */
 bool Update::updateBinary(char const *fileToSendToDC) {
     qInfo() << "UPDATING DEVICE CONTROLLER BINARY" << fileToSendToDC;