diff --git a/src/gfn/samplers.py b/src/gfn/samplers.py
index 68b052a6..f22fa06e 100644
--- a/src/gfn/samplers.py
+++ b/src/gfn/samplers.py
@@ -7,7 +7,7 @@
 from gfn.containers import Trajectories
 from gfn.env import Env
 from gfn.modules import GFNModule
-from gfn.states import States
+from gfn.states import States, stack_states
 
 
 class Sampler:
@@ -140,6 +140,8 @@ def sample_trajectories(
             else states.is_sink_state
         )
 
+        trajectories_states_b: List[States] = [states]
+
         trajectories_states: List[TT["n_trajectories", "state_shape", torch.float]] = [
             states.tensor
         ]
@@ -220,9 +222,18 @@ def sample_trajectories(
             dones = dones | new_dones
 
             trajectories_states += [states.tensor]
+            trajectories_states_b += [states]
+
+        # New Method
+        trajectories_states_b = stack_states(trajectories_states_b)
+
+        # Old Method
+        trajectories_states = env.states_from_tensor(
+            torch.stack(trajectories_states, dim=0))
+
+        assert (trajectories_states_b.tensor == trajectories_states.tensor).sum() == trajectories_states.tensor.numel()
+        assert (trajectories_states_b.forward_masks == trajectories_states.forward_masks).sum() == trajectories_states.forward_masks.numel()
 
-        trajectories_states = torch.stack(trajectories_states, dim=0)
-        trajectories_states = env.states_from_tensor(trajectories_states)
         trajectories_actions = env.Actions.stack(trajectories_actions)
         trajectories_logprobs = torch.stack(trajectories_logprobs, dim=0)