diff --git a/.readthedocs.yml b/.readthedocs.yml
index add282fa..08a36676 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -14,5 +14,7 @@ python:
   version: 3.7
   install:
     - requirements: docs/requirements.txt
+    # docs/conf.py is importing mongoengine
+    # so mongoengine needs to be installed as well
     - method: setuptools
       path: .