diff --git a/docs/guide/custom_env.rst b/docs/guide/custom_env.rst
index 5c6ab016d..1a0ac9b23 100644
--- a/docs/guide/custom_env.rst
+++ b/docs/guide/custom_env.rst
@@ -4,7 +4,7 @@
 Custom Environment
 ==================
 
-The easiest way to add support for a custom environment is to edit
+The easiest way to add support for a custom or external environment is to import it using the ``--gym-packages my_package`` argument or to edit
 ``rl_zoo3/import_envs.py`` and register your environment here. Then, you
 need to add a section for it in the hyperparameters file
 (``hyperparams/algo.yml`` or a custom yaml file that you can specify