diff --git a/model/DataExtension.php b/model/DataExtension.php
index ed94bc317..9ce91ad1b 100644
--- a/model/DataExtension.php
+++ b/model/DataExtension.php
@@ -58,7 +58,7 @@ abstract class DataExtension extends Extension {
 	 * @param $validationResult Local validation result
 	 * @throws ValidationException
 	 */
-	public function validate(ValidationResult &$validationResult) {
+	public function validate(ValidationResult $validationResult) {
 	}
 	
 	/**