diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index cb936316..11058302 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,7 +1,7 @@
 ---
 repos:
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: 'v0.4.1'
+    rev: 'v0.5.4'
     hooks:
       - id: ruff
         args: [--fix, --exit-non-zero-on-fix]
diff --git a/canaille/backends/__init__.py b/canaille/backends/__init__.py
index 58b7b9f0..dba05c1e 100644
--- a/canaille/backends/__init__.py
+++ b/canaille/backends/__init__.py
@@ -8,16 +8,16 @@ from canaille.app import classproperty
 
 
 class Backend:
-    instance = None
+    _instance = None
 
     def __init__(self, config):
         self.config = config
-        Backend.instance = self
+        Backend._instance = self
         self.register_models()
 
     @classproperty
     def instance(cls):
-        return cls.instance
+        return cls._instance
 
     def init_app(self, app):
         @app.before_request
diff --git a/tests/conftest.py b/tests/conftest.py
index 8411219d..165cfd34 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -40,6 +40,8 @@ def pytest_generate_tests(metafunc):
     backends = available_backends()
     if metafunc.config.getoption("backend"):  # pragma: no cover
         backends &= set(metafunc.config.getoption("backend"))
+
+    # sort so the backend list is deterministic. This makes pytest-xdist discovery possible
     backends = sorted(backends)
 
     # tests in tests.backends.BACKENDNAME should only run one backend