diff --git a/torchrl/envs/transforms/transforms.py b/torchrl/envs/transforms/transforms.py
index 1322f627ea5..99741a8add8 100644
--- a/torchrl/envs/transforms/transforms.py
+++ b/torchrl/envs/transforms/transforms.py
@@ -1547,6 +1547,15 @@ def __init__(
         if cat_dim > 0:
             raise ValueError(self._CAT_DIM_ERR)
         self.cat_dim = cat_dim
+        for in_key in self.in_keys:
+            buffer_name = f"_cat_buffers_{in_key}"
+            setattr(
+                self,
+                buffer_name,
+                torch.nn.parameter.UninitializedBuffer(
+                    device=torch.device("cpu"), dtype=torch.get_default_dtype()
+                ),
+            )
 
     def reset(self, tensordict: TensorDictBase) -> TensorDictBase:
         """Resets _buffers."""
@@ -1554,12 +1563,10 @@ def reset(self, tensordict: TensorDictBase) -> TensorDictBase:
         if len(tensordict.batch_size) < 1 or tensordict.batch_size[0] == 1:
             for in_key in self.in_keys:
                 buffer_name = f"_cat_buffers_{in_key}"
-                try:
-                    buffer = getattr(self, buffer_name)
-                    buffer.fill_(0.0)
-                except AttributeError:
-                    # we'll instantiate later, when needed
-                    pass
+                buffer = getattr(self, buffer_name)
+                if isinstance(buffer, torch.nn.parameter.UninitializedBuffer):
+                    continue
+                buffer.fill_(0.0)
 
         # Batched environments
         else:
@@ -1573,12 +1580,10 @@ def reset(self, tensordict: TensorDictBase) -> TensorDictBase:
             )
             for in_key in self.in_keys:
                 buffer_name = f"_cat_buffers_{in_key}"
-                try:
-                    buffer = getattr(self, buffer_name)
-                    buffer[_reset] = 0.0
-                except AttributeError:
-                    # we'll instantiate later, when needed
-                    pass
+                buffer = getattr(self, buffer_name)
+                if isinstance(buffer, torch.nn.parameter.UninitializedBuffer):
+                    continue
+                buffer[_reset] = 0.0
 
         return tensordict
 
@@ -1587,15 +1592,9 @@ def _make_missing_buffer(self, data, buffer_name):
         d = shape[self.cat_dim]
         shape[self.cat_dim] = d * self.N
         shape = torch.Size(shape)
-        self.register_buffer(
-            buffer_name,
-            torch.zeros(
-                shape,
-                dtype=data.dtype,
-                device=data.device,
-            ),
-        )
-        buffer = getattr(self, buffer_name)
+        getattr(self, buffer_name).materialize(shape)
+        buffer = getattr(self, buffer_name).to(data.dtype).to(data.device).zero_()
+        setattr(self, buffer_name, buffer)
         return buffer
 
     def _call(self, tensordict: TensorDictBase) -> TensorDictBase:
@@ -1605,12 +1604,12 @@ def _call(self, tensordict: TensorDictBase) -> TensorDictBase:
             buffer_name = f"_cat_buffers_{in_key}"
             data = tensordict[in_key]
             d = data.size(self.cat_dim)
-            try:
-                buffer = getattr(self, buffer_name)
+            buffer = getattr(self, buffer_name)
+            if isinstance(buffer, torch.nn.parameter.UninitializedBuffer):
+                buffer = self._make_missing_buffer(data, buffer_name)
+            else:
                 # shift obs 1 position to the right
                 buffer.copy_(torch.roll(buffer, shifts=-d, dims=self.cat_dim))
-            except AttributeError:
-                buffer = self._make_missing_buffer(data, buffer_name)
             # add new obs
             idx = self.cat_dim
             if idx < 0: