diff --git a/Library/Homebrew/extend/os/linux/compilers.rb b/Library/Homebrew/extend/os/linux/compilers.rb
index 8965b15100..db3e1cd00e 100644
--- a/Library/Homebrew/extend/os/linux/compilers.rb
+++ b/Library/Homebrew/extend/os/linux/compilers.rb
@@ -1,9 +1,21 @@
 # typed: strict
 # frozen_string_literal: true
 
-class CompilerSelector
-  sig { returns(String) }
-  def self.preferred_gcc
-    OS::LINUX_PREFERRED_GCC_COMPILER_FORMULA
+module OS
+  module Linux
+    module CompilerSelector
+      module ClassMethods
+        extend T::Helpers
+
+        requires_ancestor { T.class_of(::CompilerSelector) }
+
+        sig { returns(String) }
+        def preferred_gcc
+          OS::LINUX_PREFERRED_GCC_COMPILER_FORMULA
+        end
+      end
+    end
   end
 end
+
+CompilerSelector.singleton_class.prepend(OS::Linux::CompilerSelector::ClassMethods)
diff --git a/Library/Homebrew/extend/os/linux/system_config.rb b/Library/Homebrew/extend/os/linux/system_config.rb
index 90dc2de624..a9aa5213d4 100644
--- a/Library/Homebrew/extend/os/linux/system_config.rb
+++ b/Library/Homebrew/extend/os/linux/system_config.rb
@@ -51,7 +51,7 @@ module OS
           out.puts "Host glibc: #{host_glibc_version}"
           out.puts "#{::DevelopmentTools.host_gcc_path}: #{host_gcc_version}"
           out.puts "/usr/bin/ruby: #{host_ruby_version}" if RUBY_PATH != HOST_RUBY_PATH
-          ["glibc", CompilerSelector.preferred_gcc, OS::LINUX_PREFERRED_GCC_RUNTIME_FORMULA, "xorg"].each do |f|
+          ["glibc", ::CompilerSelector.preferred_gcc, OS::LINUX_PREFERRED_GCC_RUNTIME_FORMULA, "xorg"].each do |f|
             out.puts "#{f}: #{formula_linked_version(f)}"
           end
         end
diff --git a/Library/Homebrew/extend/os/mac/language/java.rb b/Library/Homebrew/extend/os/mac/language/java.rb
index 3e8192c470..d052dc9ad4 100644
--- a/Library/Homebrew/extend/os/mac/language/java.rb
+++ b/Library/Homebrew/extend/os/mac/language/java.rb
@@ -1,13 +1,26 @@
 # typed: strict
 # frozen_string_literal: true
 
-module Language
-  module Java
-    def self.java_home(version = nil)
-      openjdk = find_openjdk_formula(version)
-      return unless openjdk
+module OS
+  module Mac
+    module Language
+      module Java
+        module ClassMethods
+          extend T::Helpers
 
-      openjdk.opt_libexec/"openjdk.jdk/Contents/Home"
+          requires_ancestor { T.class_of(::Language::Java) }
+
+          sig { params(version: T.nilable(String)).returns(T.nilable(Pathname)) }
+          def java_home(version = nil)
+            openjdk = find_openjdk_formula(version)
+            return unless openjdk
+
+            openjdk.opt_libexec/"openjdk.jdk/Contents/Home"
+          end
+        end
+      end
     end
   end
 end
+
+Language::Java.singleton_class.prepend(OS::Mac::Language::Java::ClassMethods)
diff --git a/Library/Homebrew/extend/os/mac/sandbox.rb b/Library/Homebrew/extend/os/mac/sandbox.rb
index 976ede4716..a352f44fa2 100644
--- a/Library/Homebrew/extend/os/mac/sandbox.rb
+++ b/Library/Homebrew/extend/os/mac/sandbox.rb
@@ -1,9 +1,21 @@
 # typed: strict
 # frozen_string_literal: true
 
-class Sandbox
-  sig { returns(T::Boolean) }
-  def self.available?
-    File.executable?(SANDBOX_EXEC)
+module OS
+  module Mac
+    module Sandbox
+      module ClassMethods
+        extend T::Helpers
+
+        requires_ancestor { T.class_of(::Sandbox) }
+
+        sig { returns(T::Boolean) }
+        def available?
+          File.executable?(::Sandbox::SANDBOX_EXEC)
+        end
+      end
+    end
   end
 end
+
+Sandbox.singleton_class.prepend(OS::Mac::Sandbox::ClassMethods)
diff --git a/Library/Homebrew/sandbox.rb b/Library/Homebrew/sandbox.rb
index 6b3ad1dabd..1f8e29c0ae 100644
--- a/Library/Homebrew/sandbox.rb
+++ b/Library/Homebrew/sandbox.rb
@@ -10,7 +10,6 @@ require "utils/fork"
 # Helper class for running a sub-process inside of a sandboxed environment.
 class Sandbox
   SANDBOX_EXEC = "/usr/bin/sandbox-exec"
-  private_constant :SANDBOX_EXEC
 
   # This is defined in the macOS SDK but Ruby unfortunately does not expose it.
   # This value can be found by compiling a C program that prints TIOCSCTTY.