diff --git a/lib/optparse.rb b/lib/optparse.rb
index 27e0843..71a2ec2 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -1051,7 +1051,7 @@ def compsys(to, name = File.basename($0)) # :nodoc:
   end
 
   def help_exit
-    if STDOUT.tty? && (pager = ENV.values_at(*%w[RUBY_PAGER PAGER]).find {|e| e && !e.empty?})
+    if $stdout.tty? && (pager = ENV.values_at(*%w[RUBY_PAGER PAGER]).find {|e| e && !e.empty?})
       less = ENV["LESS"]
       args = [{"LESS" => "#{!less || less.empty? ? '-' : less}Fe"}, pager, "w"]
       print = proc do |f|
@@ -1060,7 +1060,7 @@ def help_exit
         # pager terminated
       end
       if Process.respond_to?(:fork) and false
-        IO.popen("-") {|f| f ? Process.exec(*args, in: f) : print.call(STDOUT)}
+        IO.popen("-") {|f| f ? Process.exec(*args, in: f) : print.call($stdout)}
         # unreachable
       end
       IO.popen(*args, &print)
@@ -1102,7 +1102,7 @@ def help_exit
   #
   Officious['*-completion-zsh'] = proc do |parser|
     Switch::OptionalArgument.new do |arg|
-      parser.compsys(STDOUT, arg)
+      parser.compsys($stdout, arg)
       exit
     end
   end
diff --git a/test/optparse/test_optparse.rb b/test/optparse/test_optparse.rb
index 7f35cb4..d50203b 100644
--- a/test/optparse/test_optparse.rb
+++ b/test/optparse/test_optparse.rb
@@ -184,10 +184,9 @@ def test_help_pager
       File.open(File.join(dir, "options.rb"), "w") do |f|
         f.puts "#{<<~"begin;"}\n#{<<~'end;'}"
         begin;
-          stdout = STDOUT.dup
+          stdout = $stdout.dup
           def stdout.tty?; true; end
-          Object.__send__(:remove_const, :STDOUT)
-          STDOUT = stdout
+          $stdout = stdout
           ARGV.options do |opt|
           end;
           100.times {|i| f.puts "  opt.on('--opt-#{i}') {}"}