diff --git a/pytest.ini b/pytest.ini
index 78710566b..677aa6d0f 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -38,3 +38,7 @@ filterwarnings =
     ignore:.*attribute in acme.client is deprecated:DeprecationWarning
     ignore:.*acme.mixins is deprecated:DeprecationWarning
     ignore:.*Authorization.combinations is deprecated:DeprecationWarning
+# If an individual test takes more than 5 minutes (300 seconds), I think we can
+# assume something has gone very wrong.
+timeout = 300
+timeout_method = thread
diff --git a/tox.ini b/tox.ini
index bf57afc49..0670b7ee2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -41,7 +41,6 @@ commands =
 # https://github.com/certbot/certbot/issues/7745.
 recreate = true
 setenv =
-    PYTEST_ADDOPTS = {env:PYTEST_ADDOPTS:--timeout=300}
     PYTHONHASHSEED = 0
 
 [testenv:oldest]