diff --git a/src/filelock/_api.py b/src/filelock/_api.py
index 9c40003..273b82e 100644
--- a/src/filelock/_api.py
+++ b/src/filelock/_api.py
@@ -56,7 +56,7 @@ def __init__(self, lock_file: str | os.PathLike[Any], timeout: float = -1) -> No
         self._lock_file_fd: int | None = None
 
         # The default timeout value.
-        self.timeout: float = timeout
+        self._timeout: float = timeout
 
         # We use this lock primarily for the lock counter.
         self._thread_lock: Lock = Lock()