diff --git a/atom/browser/ui/message_box_win.cc b/atom/browser/ui/message_box_win.cc
index 051f8f5eff6c..ecdc96770bb2 100644
--- a/atom/browser/ui/message_box_win.cc
+++ b/atom/browser/ui/message_box_win.cc
@@ -78,9 +78,9 @@ int ShowMessageBoxUTF16(HWND parent,
                         const base::string16& message,
                         const base::string16& detail,
                         const gfx::ImageSkia& icon) {
-  TASKDIALOG_FLAGS flags = TDF_SIZE_TO_CONTENT;  // show all content.
-  if (cancel_id != 0)
-    flags |= TDF_ALLOW_DIALOG_CANCELLATION;  // allow dialog to be cancelled.
+  TASKDIALOG_FLAGS flags =
+      TDF_SIZE_TO_CONTENT | // Show all content.
+      TDF_ALLOW_DIALOG_CANCELLATION; // Allow canceling the dialog.
 
   TASKDIALOGCONFIG config = { 0 };
   config.cbSize     = sizeof(config);
diff --git a/atom/renderer/lib/override.coffee b/atom/renderer/lib/override.coffee
index d8c6c0a86d79..a413178442f2 100644
--- a/atom/renderer/lib/override.coffee
+++ b/atom/renderer/lib/override.coffee
@@ -80,12 +80,15 @@ window.alert = (message, title='') ->
   buttons = ['OK']
   message = message.toString()
   dialog.showMessageBox remote.getCurrentWindow(), {message, title, buttons}
+  # Alert should always return undefined.
+  return
 
 # And the confirm().
 window.confirm = (message, title='') ->
   dialog = remote.require 'dialog'
   buttons = ['OK', 'Cancel']
-  not dialog.showMessageBox remote.getCurrentWindow(), {message, title, buttons}
+  cancelId = 1
+  not dialog.showMessageBox remote.getCurrentWindow(), {message, title, buttons, cancelId}
 
 # But we do not support prompt().
 window.prompt = ->