diff --git a/lerobot/common/datasets/abstract.py b/lerobot/common/datasets/abstract.py
index af30cf8c..5db9de86 100644
--- a/lerobot/common/datasets/abstract.py
+++ b/lerobot/common/datasets/abstract.py
@@ -54,7 +54,7 @@ class AbstractExperienceReplay(TensorDictReplayBuffer):
         return {
             ("observation", "state"): "b c -> 1 c",
             ("observation", "image"): "b c h w -> 1 c 1 1",
-            ("action"): "b c -> 1 c",
+            "action": "b c -> 1 c",
         }
 
     @property
diff --git a/lerobot/common/datasets/aloha.py b/lerobot/common/datasets/aloha.py
index 7397327d..f9351e20 100644
--- a/lerobot/common/datasets/aloha.py
+++ b/lerobot/common/datasets/aloha.py
@@ -114,7 +114,7 @@ class AlohaExperienceReplay(AbstractExperienceReplay):
     def stats_patterns(self) -> dict:
         d = {
             ("observation", "state"): "b c -> 1 c",
-            ("action"): "b c -> 1 c",
+            "action": "b c -> 1 c",
         }
         for cam in CAMERAS[self.dataset_id]:
             d[("observation", "image", cam)] = "b c h w -> 1 c 1 1"