diff --git a/lib/concurrent-ruby/concurrent/executor/serialized_execution.rb b/lib/concurrent-ruby/concurrent/executor/serialized_execution.rb
index 4db7c7f0c..c496afee6 100644
--- a/lib/concurrent-ruby/concurrent/executor/serialized_execution.rb
+++ b/lib/concurrent-ruby/concurrent/executor/serialized_execution.rb
@@ -32,6 +32,8 @@ def call
     #
     # @raise [ArgumentError] if no task is given
     def post(executor, *args, &task)
+      raise ArgumentError.new('no block given') unless block_given?
+
       posts [[executor, args, task]]
       true
     end