diff --git a/register-styles.html b/register-styles.html
index c35096d..4a9cf62 100644
--- a/register-styles.html
+++ b/register-styles.html
@@ -19,7 +19,7 @@
    * @param {String} themeFor The local/tag name of the component type to register the styles for
    * @param {CSSResult | CSSResult[]} styles The CSS style rules to be registered for the component type
    * matching themeFor and included in the local scope of each component instance
-   * @param {Object} [options] Additional options
+   * @param {Object=} options Additional options
    * @return {void}
    */
   Vaadin.registerStyles = (themeFor, styles, options) => {