diff --git a/docs/api/dialog.md b/docs/api/dialog.md
index 80a5289e93f5..ecab70a59153 100644
--- a/docs/api/dialog.md
+++ b/docs/api/dialog.md
@@ -87,6 +87,7 @@ will be passed via `callback(filename)`
   `"warning"`. On Windows, "question" displays the same icon as "info", unless
   you set an icon using the "icon" option.
   * `buttons` Array - Array of texts for buttons.
+  * `defaultButtonIndex` Integer - Index of the button in the buttons array which will be selected by default when the message box opens.
   * `title` String - Title of the message box, some platforms will not show it.
   * `message` String - Content of the message box.
   * `detail` String - Extra information of the message.