diff --git a/optuna_dashboard/_preferential_history.py b/optuna_dashboard/_preferential_history.py
index a246c166..6b81b9bb 100644
--- a/optuna_dashboard/_preferential_history.py
+++ b/optuna_dashboard/_preferential_history.py
@@ -3,7 +3,6 @@ from __future__ import annotations
 from dataclasses import dataclass
 from datetime import datetime
 import json
-from typing import Any
 from typing import TYPE_CHECKING
 import uuid
 
@@ -31,9 +30,6 @@ if TYPE_CHECKING:
         },
     )
     History = ChooseWorstHistory
-else:
-    ChooseWorstHistory = Any
-    History = Any
 
 
 @dataclass
diff --git a/optuna_dashboard/_serializer.py b/optuna_dashboard/_serializer.py
index a0999b1f..06b53c42 100644
--- a/optuna_dashboard/_serializer.py
+++ b/optuna_dashboard/_serializer.py
@@ -16,8 +16,6 @@ from . import _note as note
 from ._form_widget import get_form_widgets_json
 from ._named_objectives import get_objective_names
 from ._preferential_history import _SYSTEM_ATTR_PREFIX_HISTORY
-from ._preferential_history import ChooseWorstHistory
-from ._preferential_history import History
 from .artifact._backend import list_trial_artifacts
 from .preferential._study import _SYSTEM_ATTR_PREFERENTIAL_STUDY
 
@@ -26,6 +24,9 @@ if TYPE_CHECKING:
     from typing import Literal
     from typing import TypedDict
 
+    from ._preferential_history import ChooseWorstHistory
+    from ._preferential_history import History
+
     Attribute = TypedDict(
         "Attribute",
         {