diff --git a/libs/checkpoint-postgres/langgraph/checkpoint/postgres/base.py b/libs/checkpoint-postgres/langgraph/checkpoint/postgres/base.py
index 5f1c010ef..b0a0ff0f1 100644
--- a/libs/checkpoint-postgres/langgraph/checkpoint/postgres/base.py
+++ b/libs/checkpoint-postgres/langgraph/checkpoint/postgres/base.py
@@ -291,13 +291,18 @@ class BasePostgresSaver(BaseCheckpointSaver[str]):
                             # Step-based snapshot: collect this ancestor's
                             # pending_writes first (they encode the NEXT step's
                             # transition, not subsumed by the snapshot blob).
-                            for type_tag, write_blob, task_id, _idx in writes_by_cid.get(
-                                cid, []
-                            ):
+                            for (
+                                type_tag,
+                                write_blob,
+                                task_id,
+                                _idx,
+                            ) in writes_by_cid.get(cid, []):
                                 val = self.serde.loads_typed((type_tag, write_blob))
                                 collected.append((task_id, channel, val))
                             collected.reverse()
-                            return _ChannelWritesHistory(seed=blob_value, writes=collected)
+                            return _ChannelWritesHistory(
+                                seed=blob_value, writes=collected
+                            )
                         # Pre-delta blob: subsumes this ancestor's writes.
                         collected.reverse()
                         return _ChannelWritesHistory(seed=blob_value, writes=collected)
diff --git a/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py b/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
index d23633526..7001a5e5f 100644
--- a/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
+++ b/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
@@ -33,7 +33,11 @@ from langchain_core.load.load import Reviver
 from langgraph.checkpoint.serde import _msgpack as _lg_msgpack
 from langgraph.checkpoint.serde.base import SerializerProtocol
 from langgraph.checkpoint.serde.event_hooks import emit_serde_event
-from langgraph.checkpoint.serde.types import DELTA_SENTINEL, SendProtocol, _DeltaSnapshot
+from langgraph.checkpoint.serde.types import (
+    DELTA_SENTINEL,
+    SendProtocol,
+    _DeltaSnapshot,
+)
 from langgraph.store.base import Item
 
 if TYPE_CHECKING: