diff --git a/tox.ini b/tox.ini
index 38682615f..d4157860d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,7 @@ envlist =
        base
        dist
        docs
+isolated_build = true
 
 [testenv]
 commands = python -W error::DeprecationWarning -W error::PendingDeprecationWarning runtests.py --coverage {posargs}