diff --git a/libs/langgraph/langgraph/pregel/loop.py b/libs/langgraph/langgraph/pregel/loop.py
index ff196a778..8f3331349 100644
--- a/libs/langgraph/langgraph/pregel/loop.py
+++ b/libs/langgraph/langgraph/pregel/loop.py
@@ -600,7 +600,7 @@ class PregelLoop(LoopProtocol):
             )
         )
         # this can be set only when there are input_writes
-        updated_channels: set[str] | None = None
+        updated_channels: Union[set[str]] = None
 
         # map command to writes
         if isinstance(self.input, Command):