diff --git a/src/Util/DateTimeFormat.php b/src/Util/DateTimeFormat.php
index d2a96d0357..292fc6150f 100644
--- a/src/Util/DateTimeFormat.php
+++ b/src/Util/DateTimeFormat.php
@@ -34,7 +34,7 @@ class DateTimeFormat
 	const ATOM  = 'Y-m-d\TH:i:s\Z';
 	const MYSQL = 'Y-m-d H:i:s';
 	const HTTP  = 'D, d M Y H:i:s \G\M\T';
-	const API   = 'Y-m-d\TH:i:s.000\Z';
+	const API   = 'Y-m-d\TH:i:s.v\Z';
 
 	/**
 	 * convert() shorthand for UTC.