diff --git a/tksheet/row_index.py b/tksheet/row_index.py
index 6e831bd..a51b878 100644
--- a/tksheet/row_index.py
+++ b/tksheet/row_index.py
@@ -2485,7 +2485,7 @@ def ancestors_all_open(self, iid: str, stop_at: str | Node = "") -> bool:
                 if iid not in self.tree_open_ids:
                     return False
             return True
-        return all(iid in self.tree_open_ids for iid in self.get_iid_ancestors(iid))
+        return all(map(self.tree_open_ids.__contains__, self.get_iid_ancestors(iid)))
 
     def get_iid_ancestors(self, iid: str) -> Generator[str]:
         if self.tree[iid].parent: