diff --git a/extra/setup-py.test/setup.py b/extra/setup-py.test/setup.py
index d0560ce1f5f..97883852e2e 100644
--- a/extra/setup-py.test/setup.py
+++ b/extra/setup-py.test/setup.py
@@ -1,4 +1,5 @@
 import sys
+
 from distutils.core import setup
 
 if __name__ == "__main__":
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index f4818c861cf..91ad3f094ff 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -538,11 +538,7 @@ def _is_in_confcutdir(self, path: Path) -> bool:
         """
         if self._confcutdir is None:
             return True
-        try:
-            path.relative_to(self._confcutdir)
-        except ValueError:
-            return False
-        return True
+        return path not in self._confcutdir.parents
 
     def _try_load_conftest(
         self, anchor: Path, importmode: Union[str, ImportMode], rootpath: Path