diff --git a/tox.ini b/tox.ini
index dfe027b8977..05a37abb024 100644
--- a/tox.ini
+++ b/tox.ini
@@ -149,6 +149,9 @@ commands = {posargs}
 [testenv:docs]
 basepython = python3
 envdir = {toxworkdir}/docs
+# Do not remove requirements.txt from deps list as without it
+# upper constraints will not be used for deps listed in requirements.txt
+# and may cause issues
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/train}
   -r{toxinidir}/doc/requirements.txt