diff --git a/front_end/ui/Dialog.js b/front_end/ui/Dialog.js
index d39421fd..3cdfa26 100644
--- a/front_end/ui/Dialog.js
+++ b/front_end/ui/Dialog.js
@@ -74,7 +74,7 @@
 
   /**
    * @override
-   * @param {!Document|!Element=} where
+   * @param {(!Document|!Element)=} where
    */
   show(where) {
     const document = /** @type {!Document} */ (