diff --git a/inc/class-async-calls.php b/inc/class-async-calls.php
index 2c5de4c..af15055 100644
--- a/inc/class-async-calls.php
+++ b/inc/class-async-calls.php
@@ -162,7 +162,7 @@ class Async_Calls {
 	 * @param integer $parallel_threads The number of parallel threads to be run.
 	 * @return true|\WP_Error
 	 */
-	public static function run($id, $args, $total, $chunk_size = 10, $parallel_threads = 3): void {
+	public static function run($id, $args, $total, $chunk_size = 10, $parallel_threads = 3) {
 
 		$client = self::get_client();