diff --git a/tox.ini b/tox.ini
index 249f97c..a259a48 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,13 +5,15 @@ minversion = 3.2
 tox_pip_extensions_ext_venv_update = true
 toxworkdir={env:TOX_WORK_DIR:.tox}
 
-
 [testenv]
 deps =
 commands =
 	pytest {posargs}
 usedevelop = True
 extras = testing
+setenv =
+	# workaround pypa/pip#9143
+	PIP_USE_DEPRECATED=legacy-resolver
 
 [testenv:docs]
 extras =