diff --git a/optuna_dashboard/_app.py b/optuna_dashboard/_app.py
index ac31e857..140ad8b1 100644
--- a/optuna_dashboard/_app.py
+++ b/optuna_dashboard/_app.py
@@ -12,6 +12,7 @@ import typing
 from typing import Any
 from typing import Callable
 from typing import cast
+from typing import Dict
 from typing import Optional
 from typing import TypeVar
 from typing import Union
@@ -48,7 +49,7 @@ if typing.TYPE_CHECKING:
     except ImportError:
         FrozenStudy = None  # type: ignore
 
-BottleViewReturn = Union[str, bytes, dict[str, Any], BaseResponse]
+BottleViewReturn = Union[str, bytes, Dict[str, Any], BaseResponse]
 BottleView = TypeVar("BottleView", bound=Callable[..., BottleViewReturn])
 
 logger = logging.getLogger(__name__)
diff --git a/optuna_dashboard/_cached_extra_study_property.py b/optuna_dashboard/_cached_extra_study_property.py
index 105a1428..c8af8ec5 100644
--- a/optuna_dashboard/_cached_extra_study_property.py
+++ b/optuna_dashboard/_cached_extra_study_property.py
@@ -2,21 +2,27 @@ from __future__ import annotations
 
 import copy
 import threading
+from typing import List
 from typing import Optional
+from typing import Set
+from typing import Tuple
+from typing import TYPE_CHECKING
 
 from optuna.distributions import BaseDistribution
 from optuna.trial import FrozenTrial
 from optuna.trial import TrialState
 
 
-SearchSpaceSetT = set[tuple[str, BaseDistribution]]
-SearchSpaceListT = list[tuple[str, BaseDistribution]]
-
 #  In-memory cache
 cached_extra_study_property_cache_lock = threading.Lock()
 cached_extra_study_property_cache: dict[int, "_CachedExtraStudyProperty"] = {}
 
 
+if TYPE_CHECKING:
+    SearchSpaceSetT = Set[Tuple[str, BaseDistribution]]
+    SearchSpaceListT = List[Tuple[str, BaseDistribution]]
+
+
 def get_cached_extra_study_property(
     study_id: int, trials: list[FrozenTrial]
 ) -> tuple[SearchSpaceListT, SearchSpaceListT, list[tuple[str, bool]], bool]:
diff --git a/visual_regression_test.py b/visual_regression_test.py
index 89e70f23..a8b16502 100644
--- a/visual_regression_test.py
+++ b/visual_regression_test.py
@@ -1,4 +1,5 @@
 from __future__ import annotations
+
 import argparse
 import asyncio
 import os