diff --git a/optuna_dashboard/streamlit/_streamlit_helper.py b/optuna_dashboard/streamlit/_streamlit_helper.py
index 252c0901..45a29ee7 100644
--- a/optuna_dashboard/streamlit/_streamlit_helper.py
+++ b/optuna_dashboard/streamlit/_streamlit_helper.py
@@ -15,6 +15,7 @@ if TYPE_CHECKING:
     from typing import Callable
     from typing import Optional
     from typing import Sequence
+    from typing import Union
 
     from .._form_widget import ChoiceWidgetJSON
     from .._form_widget import SliderWidgetJSON
@@ -43,10 +44,12 @@ def _format_description(description: Optional[str]) -> str:
 
 
 def _render_widgets(
-    widgets: Sequence[ChoiceWidgetJSON | SliderWidgetJSON | TextInputWidgetJSON | UserAttrRefJSON],
+    widgets: Sequence[
+        Union[ChoiceWidgetJSON, SliderWidgetJSON, TextInputWidgetJSON, UserAttrRefJSON]
+    ],
     trial: FrozenTrial,
-) -> tuple[bool, list[Optional[str | float]]]:
-    values: list[Optional[str | float]] = []
+) -> tuple[bool, list[Optional[Union[str, float]]]]:
+    values: list[Optional[Union[str, float]]] = []
 
     with st.form("user_input", clear_on_submit=False):
         for widget in widgets:
diff --git a/python_tests/streamlit/test_streamlit_helper.py b/python_tests/streamlit/test_streamlit_helper.py
index a994c76e..8f324820 100644
--- a/python_tests/streamlit/test_streamlit_helper.py
+++ b/python_tests/streamlit/test_streamlit_helper.py
@@ -1,5 +1,6 @@
 import itertools
 from typing import Sequence
+from typing import Union
 
 import optuna
 from optuna_dashboard import ChoiceWidget
@@ -59,7 +60,7 @@ for r in range(len(widget_list) + 1):
 
 @pytest.mark.parametrize("widgets", widgets_combinations_for_user_attr)
 def test_render_user_attr_form_widgets(
-    widgets: Sequence[ChoiceWidget | SliderWidget | TextInputWidget],
+    widgets: Sequence[Union[ChoiceWidget, SliderWidget, TextInputWidget]],
 ) -> None:
     study = optuna.create_study()
     register_user_attr_form_widgets(study, widgets)  # type: ignore
@@ -76,7 +77,7 @@ for r in range(1, len(widget_list) + 1):
 
 @pytest.mark.parametrize("widgets", widgets_combinations_for_objective)
 def test_render_objective_form_widgets(
-    widgets: Sequence[ChoiceWidget | SliderWidget | TextInputWidget],
+    widgets: Sequence[Union[ChoiceWidget, SliderWidget, TextInputWidget]],
 ) -> None:
     study = optuna.create_study(directions=["maximize"] * len(widgets))
     register_objective_form_widgets(study, widgets)  # type: ignore