diff --git a/pyproject.toml b/pyproject.toml
index 4bdbe1b4..1b23a4bc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -43,6 +43,8 @@ sqlformat = "sqlparse.__main__:main"
 dev = [
     "flake8",
     "build",
+    "virtualenv<20.22.0",   # 20.22.0 dropped Python 3.6 support
+    "tox<4.5.0",  # >=4.5.0 requires virtualenv>=20.22
 ]
 test = [
     "pytest",
diff --git a/tox.ini b/tox.ini
index 0087d50e..19d17327 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,11 +1,12 @@
 [tox]
 skip_missing_interpreters = True
 envlist =
-    py35
     py36
     py37
     py38
-    pypy3
+    py39
+    py310
+    py311
     flake8
 
 [testenv]