diff --git a/src/uproot/reading.py b/src/uproot/reading.py
index 2fe169345..455943c04 100644
--- a/src/uproot/reading.py
+++ b/src/uproot/reading.py
@@ -1405,7 +1405,8 @@ def __init__(self, path, cursor, context, file, parent):
         if self._fSeekKeys == 0:
             self._header_key = None
             self._keys = []
-
+            self._keys_lookup = {}
+            self._len = None
         else:
             keys_start = self._fSeekKeys
             keys_stop = min(keys_start + self._fNbytesKeys + 8, file.fEND)