diff --git a/lib/Service/RecommendedFile.php b/lib/Service/RecommendedFile.php
index 30023f55..4197ec6c 100644
--- a/lib/Service/RecommendedFile.php
+++ b/lib/Service/RecommendedFile.php
@@ -83,6 +83,7 @@ public function setHasPreview(bool $state) {
 		$this->hasPreview = $state;
 	}
 
+	#[\ReturnTypeWillChange]
 	public function jsonSerialize() {
 		return [
 			'id' => $this->getId(),