diff --git a/Library/Homebrew/rubocops/cask/extend/string.rb b/Library/Homebrew/rubocops/cask/extend/string.rb
deleted file mode 100644
index 3f71c87c2f..0000000000
--- a/Library/Homebrew/rubocops/cask/extend/string.rb
+++ /dev/null
@@ -1,12 +0,0 @@
-# typed: strict
-# frozen_string_literal: true
-
-# Utility method extensions for String.
-class String
-  extend T::Sig
-
-  sig { returns(String) }
-  def undent
-    gsub(/^.{#{(slice(/^ +/) || '').length}}/, "")
-  end
-end
diff --git a/Library/Homebrew/rubocops/rubocop-cask.rb b/Library/Homebrew/rubocops/rubocop-cask.rb
index b17c9c4494..ed7b7fe749 100644
--- a/Library/Homebrew/rubocops/rubocop-cask.rb
+++ b/Library/Homebrew/rubocops/rubocop-cask.rb
@@ -8,7 +8,6 @@ require_relative "cask/constants/stanza"
 require_relative "cask/ast/stanza"
 require_relative "cask/ast/cask_header"
 require_relative "cask/ast/cask_block"
-require_relative "cask/extend/string"
 require_relative "cask/extend/node"
 require_relative "cask/mixin/cask_help"
 require_relative "cask/mixin/on_homepage_stanza"