diff --git a/tox.ini b/tox.ini
index 18de8445..6f075229 100644
--- a/tox.ini
+++ b/tox.ini
@@ -68,7 +68,7 @@ set_env =
     {[testenv]set_env} 
     LIBJUJU_VERSION_SPECIFIER = {env:LIBJUJU_VERSION_SPECIFIER:3.2.2}
 commands =
-    poetry run pytest --numprocesses=auto --cov=src --ignore={[vars]tests_path}/integration/ {posargs}
+    poetry run pytest --numprocesses=12 --cov=src --ignore={[vars]tests_path}/integration/ {posargs}
 
 [testenv:integration]
 description = Run integration tests