diff --git a/libs/langchain/langchain/chat_models/vertexai.py b/libs/langchain/langchain/chat_models/vertexai.py
index d6010e27fc776..2902945cc2c60 100644
--- a/libs/langchain/langchain/chat_models/vertexai.py
+++ b/libs/langchain/langchain/chat_models/vertexai.py
@@ -242,7 +242,7 @@ def _stream(
     ) -> Iterator[ChatGenerationChunk]:
         question = _get_question(messages)
         history = _parse_chat_history(messages[:-1])
-        params = self._prepare_params(stop=stop, **kwargs)
+        params = self._prepare_params(stop=stop, stream=True, **kwargs)
         examples = kwargs.get("examples", None)
         if examples:
             params["examples"] = _parse_examples(examples)