diff --git a/README.md b/README.md
index 92800ed..820188a 100644
--- a/README.md
+++ b/README.md
@@ -72,7 +72,7 @@ rescue LoadError
 end
 
 class MyEngine < ::Rails::Engine
-  config.factory_bot.definition_file_paths =
+  config.factory_bot.definition_file_paths +=
     [File.expand_path('../factories', __FILE__)] if defined?(FactoryBotRails)
 end
 ```