diff --git a/lerobot/common/envs/simxarm.py b/lerobot/common/envs/simxarm.py
index 02ec115c7..d06126257 100644
--- a/lerobot/common/envs/simxarm.py
+++ b/lerobot/common/envs/simxarm.py
@@ -168,23 +168,36 @@ def _step(self, tensordict: TensorDict):
     def _make_spec(self):
         obs = {}
         if self.from_pixels:
+            image_shape = (3, self.image_size, self.image_size)
+            if self.num_prev_obs > 0:
+                image_shape = (self.num_prev_obs + 1, *image_shape)
+
             obs["image"] = BoundedTensorSpec(
                 low=0,
                 high=255,
-                shape=(3, self.image_size, self.image_size),
+                shape=image_shape,
                 dtype=torch.uint8,
                 device=self.device,
             )
             if not self.pixels_only:
+                state_shape = (len(self._env.robot_state),)
+                if self.num_prev_obs > 0:
+                    state_shape = (self.num_prev_obs + 1, *state_shape)
+
                 obs["state"] = UnboundedContinuousTensorSpec(
-                    shape=(len(self._env.robot_state),),
+                    shape=state_shape,
                     dtype=torch.float32,
                     device=self.device,
                 )
         else:
             # TODO(rcadene): add observation_space achieved_goal and desired_goal?
+            state_shape = self._env.observation_space["observation"].shape
+            if self.num_prev_obs > 0:
+                state_shape = (self.num_prev_obs + 1, *state_shape)
+
             obs["state"] = UnboundedContinuousTensorSpec(
-                shape=self._env.observation_space["observation"].shape,
+                # TODO:
+                shape=state_shape,
                 dtype=torch.float32,
                 device=self.device,
             )