diff --git a/tox.ini b/tox.ini
index 2b8733d7df3..b91cfc24fd7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,6 +8,7 @@ envlist =
        base
        dist
        docs
+isolated_build = true
 
 [testenv]
 commands = python -W error::DeprecationWarning -W error::PendingDeprecationWarning runtests.py --coverage {posargs}