diff --git a/pyproject.toml b/pyproject.toml
index 88fcdbb..44d275b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -68,7 +68,7 @@ disable = "bad-continuation"
 [tool.tox]
 legacy_tox_ini = """
 [tox]
-envlist = py37,py38
+envlist = py37,py38,py39
 isolated_build = True
 [testenv]
 # whitelist_externals = poetry