diff --git a/lib/concurrent-ruby/concurrent/executor/ruby_single_thread_executor.rb b/lib/concurrent-ruby/concurrent/executor/ruby_single_thread_executor.rb
index 916337d4b..6d9f88c2c 100644
--- a/lib/concurrent-ruby/concurrent/executor/ruby_single_thread_executor.rb
+++ b/lib/concurrent-ruby/concurrent/executor/ruby_single_thread_executor.rb
@@ -1,4 +1,5 @@
 require 'concurrent/executor/ruby_thread_pool_executor'
+require 'concurrent/executor/serial_executor_service'
 
 module Concurrent
 
@@ -6,6 +7,7 @@ module Concurrent
   # @!macro abstract_executor_service_public_api
   # @!visibility private
   class RubySingleThreadExecutor < RubyThreadPoolExecutor
+    include SerialExecutorService
 
     # @!macro single_thread_executor_method_initialize
     def initialize(opts = {})