diff --git a/buffet/commands/command_manager.cc b/buffet/commands/command_manager.cc
index 78e0dee..afdd518 100644
--- a/buffet/commands/command_manager.cc
+++ b/buffet/commands/command_manager.cc
@@ -47,7 +47,11 @@
 bool CommandManager::LoadCommands(const base::DictionaryValue& json,
                                   const std::string& category,
                                   chromeos::ErrorPtr* error) {
-  return dictionary_.LoadCommands(json, category, &base_dictionary_, error);
+  bool result =
+      dictionary_.LoadCommands(json, category, &base_dictionary_, error);
+  if (!on_command_defs_changed_.is_null())
+    on_command_defs_changed_.Run();
+  return result;
 }
 
 bool CommandManager::LoadCommands(const base::FilePath& json_file_path,
diff --git a/buffet/commands/command_manager.h b/buffet/commands/command_manager.h
index f176cad..8088e26 100644
--- a/buffet/commands/command_manager.h
+++ b/buffet/commands/command_manager.h
@@ -37,7 +37,12 @@
       const base::WeakPtr<chromeos::dbus_utils::ExportedObjectManager>&
           object_manager);
 
-  // Get the command definitions for the device.
+  // Sets callback which is called when command definitions is changed.
+  void SetOnCommandDefChanged(const base::Closure& on_command_defs_changed) {
+    on_command_defs_changed_ = on_command_defs_changed;
+  }
+
+  // Returns the command definitions for the device.
   const CommandDictionary& GetCommandDictionary() const;
 
   // Loads base/standard GCD command definitions.
@@ -91,6 +96,7 @@
   CommandDictionary dictionary_;  // Command definitions/schemas.
   CommandQueue command_queue_;
   DBusCommandDispacher command_dispatcher_;
+  base::Closure on_command_defs_changed_;
 
   DISALLOW_COPY_AND_ASSIGN(CommandManager);
 };