diff --git a/libraries/src/Date/Date.php b/libraries/src/Date/Date.php
index 2a8cc96698402..18f68548ce838 100644
--- a/libraries/src/Date/Date.php
+++ b/libraries/src/Date/Date.php
@@ -466,7 +466,7 @@ public function toSql($local = false, DatabaseDriver $db = null)
 	 */
 	public function toRFC822($local = false)
 	{
-		return $this->format(\DateTime::RFC2822, $local, false);
+		return $this->format(\DateTimeInterface::RFC2822, $local, false);
 	}
 
 	/**