diff --git a/setup.py b/setup.py
index 982bf53..42086f9 100644
--- a/setup.py
+++ b/setup.py
@@ -27,6 +27,7 @@ setup(
             "pytest",
             "pytest-xdist",
             "packaging",
+            "virtualenv<20.22",  # pin required for tests with Python 3.6 envs
         ],
     },
     python_requires=">=3.6",