diff --git a/typo3/sysext/install/Classes/Controller/LayoutController.php b/typo3/sysext/install/Classes/Controller/LayoutController.php
index 7dd54bba3f1c56c93df48f90b5c65b69c73ce8da..6f775f93b6a9a6cf2eccf610db242c6ef30d5bba 100644
--- a/typo3/sysext/install/Classes/Controller/LayoutController.php
+++ b/typo3/sysext/install/Classes/Controller/LayoutController.php
@@ -104,7 +104,12 @@ class LayoutController extends AbstractController
     public function executeSilentLegacyExtConfExtensionConfigurationUpdateAction(): ResponseInterface
     {
         $configurationManager = new ConfigurationManager();
-        $oldExtConfSettings = $configurationManager->getConfigurationValueByPath('EXT/extConf');
+        try {
+            $oldExtConfSettings = $configurationManager->getConfigurationValueByPath('EXT/extConf');
+        } catch (\RuntimeException $e) {
+            // The old 'extConf' array may not exist anymore, set to empty array if so.
+            $oldExtConfSettings = [];
+        }
         $newExtensionSettings = $configurationManager->getConfigurationValueByPath('EXTENSIONS');
         foreach ($oldExtConfSettings as $extensionName => $extensionSettings) {
             if (!array_key_exists($extensionName, $newExtensionSettings)) {