diff --git a/src/lerobot/policies/factory.py b/src/lerobot/policies/factory.py
index e5e2700c7..f2ab93b57 100644
--- a/src/lerobot/policies/factory.py
+++ b/src/lerobot/policies/factory.py
@@ -17,8 +17,9 @@
 from __future__ import annotations
 
 import logging
-from typing import Any, TypedDict
+from typing import Any, TypedDict, cast
 
+import torch
 from torch import nn
 from typing_extensions import Unpack
 
@@ -41,7 +42,7 @@ from lerobot.policies.vqbet.configuration_vqbet import VQBeTConfig
 from lerobot.processor.pipeline import RobotProcessor
 
 
-def get_policy_class(name: str) -> PreTrainedPolicy:
+def get_policy_class(name: str) -> type[PreTrainedPolicy]:
     """Get the policy's class and config class given a name (matching the policy class' `name` attribute)."""
     if name == "tdmpc":
         from lerobot.policies.tdmpc.modeling_tdmpc import TDMPCPolicy
@@ -113,6 +114,7 @@ class ProcessorConfigKwargs(TypedDict, total=False):
     postprocessor_config_filename: str | None
     preprocessor_overrides: dict[str, Any] | None
     postprocessor_overrides: dict[str, Any] | None
+    dataset_stats: dict[str, dict[str, torch.Tensor]] | None
 
 
 def make_processor(
@@ -155,49 +157,68 @@ def make_processor(
 
     # Create a new processor based on policy type
     if policy_cfg.type == "tdmpc":
+        from lerobot.policies.tdmpc.configuration_tdmpc import TDMPCConfig
         from lerobot.policies.tdmpc.processor_tdmpc import make_tdmpc_processor
 
-        processors = make_tdmpc_processor(policy_cfg, **kwargs)
+        processors = make_tdmpc_processor(
+            config=cast(TDMPCConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "diffusion":
         from lerobot.policies.diffusion.processor_diffusion import make_diffusion_processor
 
-        processors = make_diffusion_processor(policy_cfg, **kwargs)
+        processors = make_diffusion_processor(
+            cast(DiffusionConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "act":
         from lerobot.policies.act.processor_act import make_act_processor
 
-        processors = make_act_processor(policy_cfg, **kwargs)
+        processors = make_act_processor(
+            config=cast(ACTConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "vqbet":
         from lerobot.policies.vqbet.processor_vqbet import make_vqbet_processor
 
-        processors = make_vqbet_processor(policy_cfg, **kwargs)
+        processors = make_vqbet_processor(
+            config=cast(VQBeTConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "pi0":
         from lerobot.policies.pi0.processor_pi0 import make_pi0_processor
 
-        processors = make_pi0_processor(policy_cfg, **kwargs)
+        processors = make_pi0_processor(
+            config=cast(PI0Config, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "pi0fast":
         from lerobot.policies.pi0fast.processor_pi0fast import make_pi0fast_processor
 
-        processors = make_pi0fast_processor(policy_cfg, **kwargs)
+        processors = make_pi0fast_processor(
+            cast(PI0Config, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "sac":
         from lerobot.policies.sac.processor_sac import make_sac_processor
 
-        processors = make_sac_processor(policy_cfg, **kwargs)
+        processors = make_sac_processor(
+            cast(SACConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "reward_classifier":
         from lerobot.policies.sac.reward_model.processor_classifier import make_classifier_processor
 
-        processors = make_classifier_processor(policy_cfg, **kwargs)
+        processors = make_classifier_processor(
+            cast(RewardClassifierConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     elif policy_cfg.type == "smolvla":
         from lerobot.policies.smolvla.processor_smolvla import make_smolvla_processor
 
-        processors = make_smolvla_processor(policy_cfg, **kwargs)
+        processors = make_smolvla_processor(
+            cast(SmolVLAConfig, policy_cfg), dataset_stats=kwargs.get("dataset_stats")
+        )
 
     else:
         raise NotImplementedError(f"Processor for policy type '{policy_cfg.type}' is not implemented.")
@@ -258,6 +279,8 @@ def make_policy(
                 "rather than a dataset. Normalization modules inside the policy will have infinite values "
                 "by default without stats from a dataset."
             )
+        if env_cfg is None:
+            raise ValueError("env_cfg cannot be None when ds_meta is not provided")
         features = env_to_policy_features(env_cfg)
 
     cfg.output_features = {key: ft for key, ft in features.items() if ft.type is FeatureType.ACTION}