diff --git a/torchrl/data/replay_buffers/rb_prototype.py b/torchrl/data/replay_buffers/rb_prototype.py
index ab37a4a4b1a..860f5ffeb3e 100644
--- a/torchrl/data/replay_buffers/rb_prototype.py
+++ b/torchrl/data/replay_buffers/rb_prototype.py
@@ -226,7 +226,7 @@ def extend(self, tensordicts: Union[List, TensorDictBase]) -> torch.Tensor:
         else:
             stacked_td = tensordicts
 
-        index = super().extend(tensordicts)
+        index = super().extend(stacked_td)
         stacked_td.set(
             "index",
             torch.tensor(index, dtype=torch.int, device=stacked_td.device),