diff --git a/Library/Homebrew/cask/staged.rb b/Library/Homebrew/cask/staged.rb
index b0216fc344..73dd826e9a 100644
--- a/Library/Homebrew/cask/staged.rb
+++ b/Library/Homebrew/cask/staged.rb
@@ -3,6 +3,9 @@
 require "utils/user"
 
 module Cask
+  # Helper functions for staged casks.
+  #
+  # @api private
   module Staged
     def set_permissions(paths, permissions_str)
       full_paths = remove_nonexistent(paths)