diff --git a/src/Database/ISupplementalDriver.php b/src/Database/ISupplementalDriver.php
index e950c9157..12b8a43c5 100644
--- a/src/Database/ISupplementalDriver.php
+++ b/src/Database/ISupplementalDriver.php
@@ -57,7 +57,7 @@ function formatDateTime(/*\DateTimeInterface*/ $value);
 	 * Formats date-time interval for use in a SQL statement.
 	 * @return string
 	 */
-	//function formatDateInterval(\DateInterval $value);
+	function formatDateInterval(\DateInterval $value);
 
 	/**
 	 * Encodes string for use in a LIKE statement.