diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index da77b59..e888095 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -467,6 +467,8 @@ def test_start_with_starttls_false
     end
 
     def test_start_auth_plain
+      omit "This test is not supported on Windows" if /mswin|mingw/ =~ RUBY_PLATFORM
+
       port = fake_server_start(auth: 'plain')
       Net::SMTP.start('localhost', port, user: 'account', password: 'password', authtype: :plain){}