diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 3abf168d20..383579eb71 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -2822,7 +2822,12 @@ realclean: distclean
   end
 end
 
-include MakeMakefile
+# MakeMakefile::Global = #
+m = Module.new {
+  include(MakeMakefile)
+  private(*MakeMakefile.public_instance_methods(false))
+}
+include m
 
 if not $extmk and /\A(extconf|makefile).rb\z/ =~ File.basename($0)
   END {mkmf_failed($0)}
diff --git a/test/mkmf/test_mkmf.rb b/test/mkmf/test_mkmf.rb
new file mode 100644
index 0000000000..adb86eca8d
--- /dev/null
+++ b/test/mkmf/test_mkmf.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: false
+require 'test/unit'
+require 'mkmf'
+
+class TestMkmf < Test::Unit::TestCase
+  class TestGlobal < TestMkmf
+    main = TOPLEVEL_BINDING.receiver
+    MakeMakefile.public_instance_methods(false).each do |m|
+      define_method(:"test_global_#{m}") do
+        assert_respond_to(main, [m, true])
+        assert_not_respond_to(main, [m, false])
+      end
+    end
+  end
+end