diff --git a/plugins/captcha/recaptcha/recaptcha.php b/plugins/captcha/recaptcha/recaptcha.php
index d3194019f1158..b3d650a77cc44 100644
--- a/plugins/captcha/recaptcha/recaptcha.php
+++ b/plugins/captcha/recaptcha/recaptcha.php
@@ -77,15 +77,16 @@ public function onInit($id = 'dynamic_recaptcha_1')
 	 *
 	 * @param   string  $name   The name of the field.
 	 * @param   string  $id     The id of the field.
-	 * @param   string  $class  The class of the field.
+	 * @param   string  $class  The class of the field. This should be passed as
+	 *                          e.g. 'class="required"'.
 	 *
 	 * @return  string  The HTML to be embedded in the form.
 	 *
 	 * @since  2.5
 	 */
-	public function onDisplay($name, $class, $id = 'dynamic_recaptcha_1')
+	public function onDisplay($name, $id = 'dynamic_recaptcha_1', $class = '')
 	{
-		return '<div id="' . $id . '"></div>';
+		return '<div id="' . $id . '" ' . $class . '></div>';
 	}
 
 	/**