diff --git a/www/apps/book/app/basics/modules-and-services/page.mdx b/www/apps/book/app/basics/modules-and-services/page.mdx
index f8bc3ad9cc..207c704d4c 100644
--- a/www/apps/book/app/basics/modules-and-services/page.mdx
+++ b/www/apps/book/app/basics/modules-and-services/page.mdx
@@ -30,7 +30,7 @@ For example, create the directory `src/modules/hello`.
 
 ### 1. Create Main Service
 
-A module must define a service. A service is a TypeScript or JavaScript class holding methods related to a business logic or commerce functionality.
+A module must define a service. A service is a TypeScript or JavaScript class holding methods related to a business logic or commerce functionality. It must be defined at the root of your module directory under `service.ts` filename.
 
 For example, create the file `src/modules/hello/service.ts` with the following content: