diff --git a/tests/Monolog/Formatter/ElasticSearchFormatterTest.php b/tests/Monolog/Formatter/ElasticSearchFormatterTest.php
index aefdbd00..ee95191c 100644
--- a/tests/Monolog/Formatter/ElasticSearchFormatterTest.php
+++ b/tests/Monolog/Formatter/ElasticSearchFormatterTest.php
@@ -35,7 +35,7 @@ class ElasticSearchFormatterTest extends \PHPUnit\Framework\TestCase
 
         // Expected values
         $expected = $msg;
-        $expected['datetime'] = '1970-01-01T00:00:00.000000+00:00';
+        $expected['datetime'] = '1970-01-01T00:00:00+0000';
         $expected['context'] = [
             'class' => ['stdClass' => []],
             'foo' => 7,