diff --git a/lib/private/AppFramework/OCS/BaseResponse.php b/lib/private/AppFramework/OCS/BaseResponse.php
index 60a4fb57ab4db..1c7dbdad0e9d3 100644
--- a/lib/private/AppFramework/OCS/BaseResponse.php
+++ b/lib/private/AppFramework/OCS/BaseResponse.php
@@ -126,7 +126,7 @@ protected function renderResult(array $meta): string {
 	 */
 	protected function toXML(array $array, \XMLWriter $writer) {
 		foreach ($array as $k => $v) {
-			if ($k[0] === '@') {
+			if (\is_string($k) && $k[0] === '@') {
 				$writer->writeAttribute(substr($k, 1), $v);
 				continue;
 			}