diff --git a/Library/Homebrew/cask/lib/hbc/artifact/artifact.rb b/Library/Homebrew/cask/lib/hbc/artifact/artifact.rb
index b7df4b0bd0..f61e997019 100644
--- a/Library/Homebrew/cask/lib/hbc/artifact/artifact.rb
+++ b/Library/Homebrew/cask/lib/hbc/artifact/artifact.rb
@@ -1,6 +1,7 @@
 require "hbc/artifact/moved"
 
-require "hbc/utils/hash_validator"
+require "extend/hash_validator"
+using HashValidator
 
 module Hbc
   module Artifact
@@ -20,7 +21,7 @@ module Hbc
           raise CaskInvalidError.new(cask.token, "target required for #{english_name} '#{source_string}'")
         end
 
-        target_hash.extend(HashValidator).assert_valid_keys(:target)
+        target_hash.assert_valid_keys!(:target)
 
         new(cask, source_string, **target_hash)
       end
diff --git a/Library/Homebrew/cask/lib/hbc/artifact/installer.rb b/Library/Homebrew/cask/lib/hbc/artifact/installer.rb
index a3a84164e0..269e122f54 100644
--- a/Library/Homebrew/cask/lib/hbc/artifact/installer.rb
+++ b/Library/Homebrew/cask/lib/hbc/artifact/installer.rb
@@ -1,5 +1,8 @@
 require "hbc/artifact/abstract_artifact"
 
+require "extend/hash_validator"
+using HashValidator
+
 module Hbc
   module Artifact
     class Installer < AbstractArtifact
@@ -60,7 +63,7 @@ module Hbc
           raise CaskInvalidError.new(cask, "invalid 'installer' stanza: Only one of #{VALID_KEYS.inspect} is permitted.")
         end
 
-        args.extend(HashValidator).assert_valid_keys(*VALID_KEYS)
+        args.assert_valid_keys!(*VALID_KEYS)
         new(cask, **args)
       end
 
diff --git a/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb b/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb
index 0fc9eac2bb..81b6e4d116 100644
--- a/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb
+++ b/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb
@@ -1,8 +1,9 @@
+require "vendor/plist/plist"
+
 require "hbc/artifact/abstract_artifact"
 
-require "hbc/utils/hash_validator"
-
-require "vendor/plist/plist"
+require "extend/hash_validator"
+using HashValidator
 
 module Hbc
   module Artifact
@@ -10,9 +11,7 @@ module Hbc
       attr_reader :pkg_relative_path
 
       def self.from_args(cask, path, **stanza_options)
-        stanza_options.extend(HashValidator).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/lib/hbc/artifact/relocated.rb b/Library/Homebrew/cask/lib/hbc/artifact/relocated.rb
index 9195d889a7..b9d897983b 100644
--- a/Library/Homebrew/cask/lib/hbc/artifact/relocated.rb
+++ b/Library/Homebrew/cask/lib/hbc/artifact/relocated.rb
@@ -1,6 +1,7 @@
 require "hbc/artifact/abstract_artifact"
 
-require "hbc/utils/hash_validator"
+require "extend/hash_validator"
+using HashValidator
 
 module Hbc
   module Artifact
@@ -10,7 +11,7 @@ module Hbc
 
         if target_hash
           raise CaskInvalidError unless target_hash.respond_to?(:keys)
-          target_hash.extend(HashValidator).assert_valid_keys(:target)
+          target_hash.assert_valid_keys!(:target)
         end
 
         target_hash ||= {}
diff --git a/Library/Homebrew/cask/lib/hbc/system_command.rb b/Library/Homebrew/cask/lib/hbc/system_command.rb
index e1cbb3122a..a443e8d38b 100644
--- a/Library/Homebrew/cask/lib/hbc/system_command.rb
+++ b/Library/Homebrew/cask/lib/hbc/system_command.rb
@@ -3,8 +3,8 @@ require "vendor/plist/plist"
 require "shellwords"
 
 require "extend/io"
-
-require "hbc/utils/hash_validator"
+require "extend/hash_validator"
+using HashValidator
 
 module Hbc
   class SystemCommand
@@ -45,7 +45,7 @@ module Hbc
       @print_stdout = print_stdout
       @print_stderr = print_stderr
       @must_succeed = must_succeed
-      options.extend(HashValidator).assert_valid_keys(:chdir)
+      options.assert_valid_keys!(:chdir)
       @options = options
       @env = env
 
diff --git a/Library/Homebrew/cask/lib/hbc/utils/hash_validator.rb b/Library/Homebrew/cask/lib/hbc/utils/hash_validator.rb
deleted file mode 100644
index f43bf173f4..0000000000
--- a/Library/Homebrew/cask/lib/hbc/utils/hash_validator.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-module HashValidator
-  def assert_valid_keys(*valid_keys)
-    unknown_keys = keys - valid_keys
-    return if unknown_keys.empty?
-    raise %Q(Unknown keys: #{unknown_keys.inspect}. Running "brew update" will likely fix it.)
-  end
-end
diff --git a/Library/Homebrew/extend/hash_validator.rb b/Library/Homebrew/extend/hash_validator.rb
new file mode 100644
index 0000000000..c5a046f9b6
--- /dev/null
+++ b/Library/Homebrew/extend/hash_validator.rb
@@ -0,0 +1,9 @@
+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