diff --git a/docs/sources/examples/running_redis_service.rst b/docs/sources/examples/running_redis_service.rst
index 3b2f65c128..7cbc58b58a 100644
--- a/docs/sources/examples/running_redis_service.rst
+++ b/docs/sources/examples/running_redis_service.rst
@@ -67,7 +67,8 @@ Once inside our freshly created container we need to install Redis to get the
     apt-get -y install redis-server
     service redis-server stop
 
-Docker sets some environment variables in our web application container. 
+Since we used the ``--link redis:db`` option before. Docker has created some 
+environment variables in our web application container. 
 Let's inspect them with the ``env`` command.
 
 .. code-block:: bash