diff --git a/ldp/alg/callbacks.py b/ldp/alg/callbacks.py
index cbb6d16..e52d967 100644
--- a/ldp/alg/callbacks.py
+++ b/ldp/alg/callbacks.py
@@ -173,7 +173,7 @@ async def after_transition(
         # TODO: make this async?
         traj.to_jsonl(self.out_files[traj_id])
         if transition.done:
-            with Path(self.env_files[traj_id]).open() as f:
+            with Path(self.env_files[traj_id]).open("w") as f:
                 f.write(env.export_frame().model_dump_json(exclude={"state"}, indent=2))