diff --git a/apps/files_external/lib/Service/UserStoragesService.php b/apps/files_external/lib/Service/UserStoragesService.php
index 3f4d08b1ea0..04f8a321c14 100644
--- a/apps/files_external/lib/Service/UserStoragesService.php
+++ b/apps/files_external/lib/Service/UserStoragesService.php
@@ -124,6 +124,9 @@ class UserStoragesService extends StoragesService {
 	 * @throws NotFoundException if the given storage does not exist in the config
 	 */
 	public function updateStorage(StorageConfig $updatedStorage) {
+		// verify ownership through $this->isApplicable() and otherwise throws an exception
+		$this->getStorage($updatedStorage->getId());
+
 		$updatedStorage->setApplicableUsers([$this->getUser()->getUID()]);
 		return parent::updateStorage($updatedStorage);
 	}