diff --git a/libs/langgraph/langgraph/pregel/main.py b/libs/langgraph/langgraph/pregel/main.py
index 89ed674fa..09b3e6517 100644
--- a/libs/langgraph/langgraph/pregel/main.py
+++ b/libs/langgraph/langgraph/pregel/main.py
@@ -2354,7 +2354,7 @@ class Pregel(
             validate_keys(output_keys, self.channels)
         interrupt_before = interrupt_before or self.interrupt_before_nodes
         interrupt_after = interrupt_after or self.interrupt_after_nodes
-        if not isinstance(stream_mode, list):
+        if isinstance(stream_mode, str):
             stream_modes = {stream_mode}
         else:
             stream_modes = set(stream_mode)