diff --git a/src/Client.php b/src/Client.php
index ca58357..c753553 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -449,7 +449,7 @@ private function deliverResponses(string $message)
     public static function onError($level, $message, $file, $line)
     {
         $message = trim($message);
-        $code = null;
+        $code = 0;
 
         throw new ErrorException($message, $code, $level, $file, $line);
     }