diff --git a/buffet/commands/command_queue.cc b/buffet/commands/command_queue.cc
index 614261e..f4cda60 100644
--- a/buffet/commands/command_queue.cc
+++ b/buffet/commands/command_queue.cc
@@ -15,6 +15,9 @@
 
 void CommandQueue::AddOnCommandAddedCallback(const Callback& callback) {
   on_command_added_.push_back(callback);
+  // Send all pre-existed commands.
+  for (const auto& command : map_)
+    callback.Run(command.second.get());
 }
 
 void CommandQueue::AddOnCommandRemovedCallback(const Callback& callback) {