diff --git a/platform/ruby/mail_checker.tmpl.rb b/platform/ruby/mail_checker.tmpl.rb
index 39fedec7..f6b6b552 100644
--- a/platform/ruby/mail_checker.tmpl.rb
+++ b/platform/ruby/mail_checker.tmpl.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'set'
 
 module MailChecker