diff --git a/libs/vertexai/langchain_google_vertexai/llms.py b/libs/vertexai/langchain_google_vertexai/llms.py
index ca16de4a..7221c96b 100644
--- a/libs/vertexai/langchain_google_vertexai/llms.py
+++ b/libs/vertexai/langchain_google_vertexai/llms.py
@@ -215,7 +215,7 @@ def _default_params(self) -> Dict[str, Any]:
         updated_params = {}
         for param_name, param_value in params.items():
             default_value = default_params.get(param_name)
-            if param_value or default_value:
+            if param_value is not None or default_value is not None:
                 updated_params[param_name] = (
                     param_value if param_value is not None else default_value
                 )
diff --git a/libs/vertexai/tests/unit_tests/test_llm.py b/libs/vertexai/tests/unit_tests/test_llm.py
index 8d65221e..5fc23d7e 100644
--- a/libs/vertexai/tests/unit_tests/test_llm.py
+++ b/libs/vertexai/tests/unit_tests/test_llm.py
@@ -47,3 +47,9 @@ def test_vertexai_args_passed() -> None:
                     },
                 },
             )
+            assert (
+                model_instance.generate_content.call_args.kwargs["generation_config"][
+                    "temperature"
+                ]
+                == 0
+            )