diff --git a/tox.ini b/tox.ini
index 16e5e84..c701e94 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,6 +5,7 @@
 
 [tox]
 envlist = py37, py38, py39, pypy3
+isolated_build = True
 
 [gh-actions]
 python =