diff --git a/firmware-upgrade-reboot.rsc b/firmware-upgrade-reboot.rsc
index 86a9a8c5..17a6dd36 100644
--- a/firmware-upgrade-reboot.rsc
+++ b/firmware-upgrade-reboot.rsc
@@ -9,7 +9,8 @@
 # https://rsc.eworm.de/doc/firmware-upgrade-reboot.md
 
 :global GlobalFunctionsReady;
-:while ($GlobalFunctionsReady != true) do={ :delay 500ms; }
+:onerror e { :retry { :if ($GlobalFunctionsReady != true) \
+  do={ :error "Global functions not ready."; }; } delay=500ms max=20; } do={ :log error $e; };
 
 :local ExitOK false;
 :do {