diff --git a/Classes/EventListener/AbstractImageOptimizer.php b/Classes/EventListener/AbstractImageOptimizer.php
index 443af3e..7b61123 100644
--- a/Classes/EventListener/AbstractImageOptimizer.php
+++ b/Classes/EventListener/AbstractImageOptimizer.php
@@ -27,7 +27,10 @@ public function __construct()
 
     protected function isEnabled(ProcessedFile $processedFile): bool
     {
-        if (!ApplicationType::fromRequest($GLOBALS['TYPO3_REQUEST'])->isFrontend()) {
+        if (
+            !array_key_exists('TYPO3_REQUEST', $GLOBALS) ||
+            !ApplicationType::fromRequest($GLOBALS['TYPO3_REQUEST'])->isFrontend()
+        ) {
             // this is not needed for TYPO3 backend and would break deferred image processing
             return false;
         }