diff --git a/tox.ini b/tox.ini
index 1ae5e32364b6..8272774fa912 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,13 +1,8 @@
 [tox]
 minversion = 3.18.0
 envlist = py3,functional,pep8
-# Automatic envs (pyXX) will only use the python version appropriate to that
-# env and ignore basepython inherited from [testenv] if we set
-# ignore_basepython_conflict.
-ignore_basepython_conflict = True
 
 [testenv]
-basepython = python3
 usedevelop = True
 allowlist_externals =
 bash
@@ -15,6 +10,7 @@ allowlist_externals =
 rm
 env
 make
+install_command = python -I -m pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 setenv =
 VIRTUAL_ENV={envdir}
 LANGUAGE=en_US
@@ -26,8 +22,6 @@ setenv =
 # TODO(stephenfin): Remove once we bump our upper-constraint to SQLAlchemy 2.0
 SQLALCHEMY_WARN_20=1
 deps =
- -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
- -r{toxinidir}/requirements.txt
 -r{toxinidir}/test-requirements.txt
 extras =
 zvm
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