diff --git a/pyproject.toml b/pyproject.toml
index da8c0d83..f71c940b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -51,9 +51,12 @@ include = ["fusesoc", "fusesoc.capi2", "fusesoc.provider", "fusesoc.parser"]
 [project.scripts]
 fusesoc = "fusesoc.main:main"
 
+[tool.tox]
+legacy_tox_ini = """
 [tox]
-isolated_build = true
+envlist = py3
 
 [testenv]
+deps = pytest
 commands = pytest
-envlist = py3
+"""