diff --git a/src/structlog/_output.py b/src/structlog/_output.py
index b1612de6..a35df747 100644
--- a/src/structlog/_output.py
+++ b/src/structlog/_output.py
@@ -186,6 +186,8 @@ def __setstate__(self, state: Any) -> None:
         else:
             self._file = stderr
 
+        self._write = self._file.write
+        self._flush = self._file.flush
         self._lock = _get_lock_for_file(self._file)
 
     def __deepcopy__(self, memodict: dict[str, object]) -> WriteLogger: