diff --git a/pyproject.toml b/pyproject.toml
index fe4aaac..b214f6a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,7 +35,7 @@ padpo = "padpo.padpo:main"
 legacy_tox_ini = """
 [tox]
 isolated_build = True
-envlist = py37, py38
+envlist = py37, py38, py39
 
 [testenv]
 whitelist_externals =