diff --git a/libs/core/langchain_core/utils/function_calling.py b/libs/core/langchain_core/utils/function_calling.py
index 28a1ab73513..b6c902872d4 100644
--- a/libs/core/langchain_core/utils/function_calling.py
+++ b/libs/core/langchain_core/utils/function_calling.py
@@ -5,6 +5,7 @@ from __future__ import annotations
 import collections
 import inspect
 import logging
+import types
 import typing
 import uuid
 from typing import (
@@ -575,6 +576,10 @@ def _parse_google_docstring(
 
 
 def _py_38_safe_origin(origin: Type) -> Type:
+    origin_union_type_map: Dict[Type, Any] = (
+        {types.UnionType: Union} if hasattr(types, "UnionType") else {}
+    )
+
     origin_map: Dict[Type, Any] = {
         dict: Dict,
         list: List,
@@ -584,5 +589,6 @@ def _py_38_safe_origin(origin: Type) -> Type:
         collections.abc.Mapping: typing.Mapping,
         collections.abc.Sequence: typing.Sequence,
         collections.abc.MutableMapping: typing.MutableMapping,
+        **origin_union_type_map,
     }
     return cast(Type, origin_map.get(origin, origin))
diff --git a/libs/core/tests/unit_tests/utils/test_function_calling.py b/libs/core/tests/unit_tests/utils/test_function_calling.py
index daa981d3143..7c68cd24a2b 100644
--- a/libs/core/tests/unit_tests/utils/test_function_calling.py
+++ b/libs/core/tests/unit_tests/utils/test_function_calling.py
@@ -1,4 +1,5 @@
 # mypy: disable-error-code="annotation-unchecked"
+import sys
 from typing import (
     Any,
     Callable,
@@ -702,3 +703,18 @@ def test__convert_typed_dict_to_openai_function_fail(typed_dict: Type) -> None:
 
     with pytest.raises(TypeError):
         _convert_typed_dict_to_openai_function(Tool)
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 10), reason="Requires python version >= 3.10 to run."
+)
+def test_convert_union_type_py_39() -> None:
+    @tool
+    def magic_function(input: int | float) -> str:
+        """Compute a magic function."""
+        pass
+
+    result = convert_to_openai_function(magic_function)
+    assert result["parameters"]["properties"]["input"] == {
+        "anyOf": [{"type": "integer"}, {"type": "number"}]
+    }