diff --git a/Library/Homebrew/cask/artifact/abstract_uninstall.rb b/Library/Homebrew/cask/artifact/abstract_uninstall.rb
index 2635bd79d1..7b4d522a7a 100644
--- a/Library/Homebrew/cask/artifact/abstract_uninstall.rb
+++ b/Library/Homebrew/cask/artifact/abstract_uninstall.rb
@@ -6,8 +6,6 @@ require "timeout"
 require "utils/user"
 require "cask/artifact/abstract_artifact"
 require "cask/pkg"
-require "extend/hash_validator"
-using HashValidator
 
 module Cask
   module Artifact
@@ -38,7 +36,7 @@ module Cask
       attr_reader :directives
 
       def initialize(cask, directives)
-        directives.assert_valid_keys!(*ORDERED_DIRECTIVES)
+        directives.assert_valid_keys(*ORDERED_DIRECTIVES)
 
         super(cask, **directives)
         directives[:signal] = Array(directives[:signal]).flatten.each_slice(2).to_a
diff --git a/Library/Homebrew/cask/artifact/artifact.rb b/Library/Homebrew/cask/artifact/artifact.rb
index 705cc4d18a..a3b25a5972 100644
--- a/Library/Homebrew/cask/artifact/artifact.rb
+++ b/Library/Homebrew/cask/artifact/artifact.rb
@@ -3,9 +3,6 @@
 
 require "cask/artifact/moved"
 
-require "extend/hash_validator"
-using HashValidator
-
 module Cask
   module Artifact
     # Generic artifact corresponding to the `artifact` stanza.
diff --git a/Library/Homebrew/cask/artifact/installer.rb b/Library/Homebrew/cask/artifact/installer.rb
index ef20cd0bd1..735a74688f 100644
--- a/Library/Homebrew/cask/artifact/installer.rb
+++ b/Library/Homebrew/cask/artifact/installer.rb
@@ -3,9 +3,6 @@
 
 require "cask/artifact/abstract_artifact"
 
-require "extend/hash_validator"
-using HashValidator
-
 module Cask
   module Artifact
     # Artifact corresponding to the `installer` stanza.
@@ -67,7 +64,7 @@ module Cask
           )
         end
 
-        args.assert_valid_keys!(*VALID_KEYS)
+        args.assert_valid_keys(*VALID_KEYS)
         new(cask, **args)
       end
 
diff --git a/Library/Homebrew/cask/artifact/pkg.rb b/Library/Homebrew/cask/artifact/pkg.rb
index 924f731ae4..7a22057909 100644
--- a/Library/Homebrew/cask/artifact/pkg.rb
+++ b/Library/Homebrew/cask/artifact/pkg.rb
@@ -6,9 +6,6 @@ require "plist"
 require "utils/user"
 require "cask/artifact/abstract_artifact"
 
-require "extend/hash_validator"
-using HashValidator
-
 module Cask
   module Artifact
     # Artifact corresponding to the `pkg` stanza.
@@ -18,7 +15,7 @@ module Cask
       attr_reader :path, :stanza_options
 
       def self.from_args(cask, path, **stanza_options)
-        stanza_options.assert_valid_keys!(:allow_untrusted, :choices)
+        stanza_options.assert_valid_keys(:allow_untrusted, :choices)
         new(cask, path, **stanza_options)
       end
 
diff --git a/Library/Homebrew/cask/artifact/relocated.rb b/Library/Homebrew/cask/artifact/relocated.rb
index ee5ca48d73..80d2e727b1 100644
--- a/Library/Homebrew/cask/artifact/relocated.rb
+++ b/Library/Homebrew/cask/artifact/relocated.rb
@@ -3,9 +3,6 @@
 
 require "cask/artifact/abstract_artifact"
 
-require "extend/hash_validator"
-using HashValidator
-
 module Cask
   module Artifact
     # Superclass for all artifacts which have a source and a target location.
@@ -20,7 +17,7 @@ module Cask
         if target_hash
           raise CaskInvalidError unless target_hash.respond_to?(:keys)
 
-          target_hash.assert_valid_keys!(:target)
+          target_hash.assert_valid_keys(:target)
         end
 
         target_hash ||= {}
diff --git a/Library/Homebrew/cask/config.rb b/Library/Homebrew/cask/config.rb
index db28860126..ae083bf292 100644
--- a/Library/Homebrew/cask/config.rb
+++ b/Library/Homebrew/cask/config.rb
@@ -6,9 +6,6 @@ require "json"
 require "lazy_object"
 require "locale"
 
-require "extend/hash_validator"
-using HashValidator
-
 module Cask
   # Configuration for installing casks.
   #
@@ -110,8 +107,8 @@ module Cask
         return
       end
 
-      @env&.assert_valid_keys!(*self.class.defaults.keys)
-      @explicit.assert_valid_keys!(*self.class.defaults.keys)
+      @env&.assert_valid_keys(*self.class.defaults.keys)
+      @explicit.assert_valid_keys(*self.class.defaults.keys)
     end
 
     sig { returns(T::Hash[Symbol, T.any(String, Pathname, T::Array[String])]) }
diff --git a/Library/Homebrew/cask/dsl/conflicts_with.rb b/Library/Homebrew/cask/dsl/conflicts_with.rb
index 99ca4c9838..40b19f6056 100644
--- a/Library/Homebrew/cask/dsl/conflicts_with.rb
+++ b/Library/Homebrew/cask/dsl/conflicts_with.rb
@@ -3,9 +3,6 @@
 
 require "delegate"
 
-require "extend/hash_validator"
-using HashValidator
-
 module Cask
   class DSL
     # Class corresponding to the `conflicts_with` stanza.
@@ -22,7 +19,7 @@ module Cask
       ].freeze
 
       def initialize(**options)
-        options.assert_valid_keys!(*VALID_KEYS)
+        options.assert_valid_keys(*VALID_KEYS)
 
         conflicts = options.transform_values { |v| Set.new(Kernel.Array(v)) }
         conflicts.default = Set.new
diff --git a/Library/Homebrew/extend/hash_validator.rb b/Library/Homebrew/extend/hash_validator.rb
deleted file mode 100644
index 09cfbe68a3..0000000000
--- a/Library/Homebrew/extend/hash_validator.rb
+++ /dev/null
@@ -1,13 +0,0 @@
-# typed: false
-# frozen_string_literal: true
-
-module HashValidator
-  refine Hash do
-    def assert_valid_keys!(*valid_keys)
-      unknown_keys = keys - valid_keys
-      return if unknown_keys.empty?
-
-      raise ArgumentError, "invalid keys: #{unknown_keys.map(&:inspect).join(", ")}"
-    end
-  end
-end
diff --git a/Library/Homebrew/extend/hash_validator.rbi b/Library/Homebrew/extend/hash_validator.rbi
deleted file mode 100644
index 715b783813..0000000000
--- a/Library/Homebrew/extend/hash_validator.rbi
+++ /dev/null
@@ -1,6 +0,0 @@
-# typed: strict
-
-class Hash
-  sig { params(valid_keys: T.untyped).void }
-  def assert_valid_keys!(*valid_keys); end
-end
diff --git a/Library/Homebrew/system_command.rb b/Library/Homebrew/system_command.rb
index e069a4e27f..af201706d4 100644
--- a/Library/Homebrew/system_command.rb
+++ b/Library/Homebrew/system_command.rb
@@ -7,7 +7,6 @@ require "shellwords"
 
 require "extend/io"
 require "extend/predicable"
-require "extend/hash_validator"
 
 require "extend/time"