diff --git a/nox/virtualenv.py b/nox/virtualenv.py
index eba573e7..0e3bbca3 100644
--- a/nox/virtualenv.py
+++ b/nox/virtualenv.py
@@ -43,6 +43,8 @@ def __init__(self, interpreter: str) -> None:
 class ProcessEnv:
     """A environment with a 'bin' directory and a set of 'env' vars."""
 
+    location: str
+
     # Does this environment provide any process isolation?
     is_sandboxed = False