diff --git a/Library/Homebrew/cask/cmd/install.rb b/Library/Homebrew/cask/cmd/install.rb
index e19e64eb01..c4a550b5ba 100644
--- a/Library/Homebrew/cask/cmd/install.rb
+++ b/Library/Homebrew/cask/cmd/install.rb
@@ -1,6 +1,8 @@
 # typed: false
 # frozen_string_literal: true
 
+require "cask_dependent"
+
 module Cask
   class Cmd
     # Cask implementation of the `brew install` command.