diff --git a/libs/langgraph/langgraph/pregel/__init__.py b/libs/langgraph/langgraph/pregel/__init__.py
index 256ddbd6c..4dd69806d 100644
--- a/libs/langgraph/langgraph/pregel/__init__.py
+++ b/libs/langgraph/langgraph/pregel/__init__.py
@@ -2751,10 +2751,10 @@ class Pregel(PregelProtocol):
             return chunks
 
 
-def _trigger_to_nodes(nodes: dict[str, PregelNode]) -> dict[str, list[str]]:
+def _trigger_to_nodes(nodes: dict[str, PregelNode]) -> Mapping[str, list[str]]:
     """Index from a trigger to nodes that depend on it."""
     trigger_to_nodes: defaultdict[str, list[str]] = defaultdict(list)
     for name, node in nodes.items():
         for trigger in node.triggers:
             trigger_to_nodes.setdefault(trigger, []).append(name)
-    return trigger_to_nodes
+    return cast(Mapping[str, list[str]], trigger_to_nodes)
diff --git a/libs/langgraph/langgraph/pregel/algo.py b/libs/langgraph/langgraph/pregel/algo.py
index cc9a45e59..5574f4777 100644
--- a/libs/langgraph/langgraph/pregel/algo.py
+++ b/libs/langgraph/langgraph/pregel/algo.py
@@ -347,7 +347,7 @@ def prepare_next_tasks(
     store: Literal[None] = None,
     checkpointer: Literal[None] = None,
     manager: Literal[None] = None,
-    trigger_to_nodes: Optional[Mapping[str, set[str]]] = None,
+    trigger_to_nodes: Optional[Mapping[str, list[str]]] = None,
     updated_channels: Optional[set[str]] = None,
 ) -> dict[str, PregelTask]: ...
 
@@ -366,7 +366,7 @@ def prepare_next_tasks(
     store: Optional[BaseStore],
     checkpointer: Optional[BaseCheckpointSaver],
     manager: Union[None, ParentRunManager, AsyncParentRunManager],
-    trigger_to_nodes: Optional[Mapping[str, set[str]]] = None,
+    trigger_to_nodes: Optional[Mapping[str, list[str]]] = None,
     updated_channels: Optional[set[str]] = None,
 ) -> dict[str, PregelExecutableTask]: ...
 
@@ -384,7 +384,7 @@ def prepare_next_tasks(
     store: Optional[BaseStore] = None,
     checkpointer: Optional[BaseCheckpointSaver] = None,
     manager: Union[None, ParentRunManager, AsyncParentRunManager] = None,
-    trigger_to_nodes: Optional[Mapping[str, set[str]]] = None,
+    trigger_to_nodes: Optional[Mapping[str, list[str]]] = None,
     updated_channels: Optional[set[str]] = None,
 ) -> Union[dict[str, PregelTask], dict[str, PregelExecutableTask]]:
     """Prepare the set of tasks that will make up the next Pregel step.
diff --git a/libs/langgraph/langgraph/pregel/loop.py b/libs/langgraph/langgraph/pregel/loop.py
index 518372834..0cd109f23 100644
--- a/libs/langgraph/langgraph/pregel/loop.py
+++ b/libs/langgraph/langgraph/pregel/loop.py
@@ -209,7 +209,7 @@ class PregelLoop(LoopProtocol):
         manager: Union[None, AsyncParentRunManager, ParentRunManager] = None,
         input_model: Optional[Type[BaseModel]] = None,
         debug: bool = False,
-        trigger_to_nodes: Optional[Mapping[str, Sequence[str]]] = None,
+        trigger_to_nodes: Optional[Mapping[str, list[str]]] = None,
     ) -> None:
         super().__init__(
             step=0,
@@ -889,7 +889,7 @@ class SyncPregelLoop(PregelLoop, ContextManager):
         stream_keys: Union[str, Sequence[str]] = EMPTY_SEQ,
         input_model: Optional[Type[BaseModel]] = None,
         debug: bool = False,
-        trigger_to_nodes: Optional[Mapping[str, Sequence[str]]] = None,
+        trigger_to_nodes: Optional[Mapping[str, list[str]]] = None,
     ) -> None:
         super().__init__(
             input,
@@ -1032,7 +1032,7 @@ class AsyncPregelLoop(PregelLoop, AsyncContextManager):
         stream_keys: Union[str, Sequence[str]] = EMPTY_SEQ,
         input_model: Optional[Type[BaseModel]] = None,
         debug: bool = False,
-        trigger_to_nodes: Optional[Mapping[str, Sequence[str]]] = None,
+        trigger_to_nodes: Optional[Mapping[str, list[str]]] = None,
     ) -> None:
         super().__init__(
             input,