diff --git a/optuna_dashboard/_cached_extra_study_property.py b/optuna_dashboard/_cached_extra_study_property.py
index c8af8ec5..304c2a16 100644
--- a/optuna_dashboard/_cached_extra_study_property.py
+++ b/optuna_dashboard/_cached_extra_study_property.py
@@ -88,7 +88,10 @@ class _CachedExtraStudyProperty:
 
     def _update_user_attrs(self, trial: FrozenTrial) -> None:
         # TODO(c-bata): Support numpy-specific number types.
-        current_user_attrs = {k: isinstance(v, (int, float)) for k, v in trial.user_attrs.items()}
+        current_user_attrs = {
+            k: not isinstance(v, bool) and isinstance(v, (int, float))
+            for k, v in trial.user_attrs.items()
+        }
         for attr_name, current_is_sortable in current_user_attrs.items():
             is_sortable = self._union_user_attrs.get(attr_name)
             if is_sortable is None:
diff --git a/optuna_dashboard/ts/components/GraphSlice.tsx b/optuna_dashboard/ts/components/GraphSlice.tsx
index 0d2d2f90..893647e4 100644
--- a/optuna_dashboard/ts/components/GraphSlice.tsx
+++ b/optuna_dashboard/ts/components/GraphSlice.tsx
@@ -15,8 +15,7 @@ import {
 import { plotlyDarkTemplate } from "./PlotlyDarkMode"
 import {
   Target,
-  useFilteredTrials,
-  useObjectiveTargets,
+  useFilteredTrials, useObjectiveAndUserAttrTargets,
   useParamTargets,
 } from "../trialFilter"
 import { useMergedUnionSearchSpace } from "../searchSpace"
@@ -36,7 +35,7 @@ export const GraphSlice: FC<{
   const theme = useTheme()
 
   const [objectiveTargets, selectedObjective, setObjectiveTarget] =
-    useObjectiveTargets(study)
+    useObjectiveAndUserAttrTargets(study)
   const searchSpace = useMergedUnionSearchSpace(study?.union_search_space)
   const [paramTargets, selectedParamTarget, setParamTarget] =
     useParamTargets(searchSpace)
@@ -96,7 +95,7 @@ export const GraphSlice: FC<{
         >
           Slice
         </Typography>
-        {study !== null && study.directions.length !== 1 && (
+        {objectiveTargets.length !== 1 && (
           <FormControl component="fieldset">
             <FormLabel component="legend">Objective:</FormLabel>
             <Select
diff --git a/python_tests/test_cached_extra_study_property.py b/python_tests/test_cached_extra_study_property.py
index 16860586..3c00fd37 100644
--- a/python_tests/test_cached_extra_study_property.py
+++ b/python_tests/test_cached_extra_study_property.py
@@ -254,11 +254,11 @@ class _CachedExtraStudyPropertyUserAttrs(TestCase):
 
     def test_infer_sortable(self) -> None:
         user_attrs_list: list[dict[str, Any]] = [
-            {"a": 1, "b": 1, "c": 1, "d": "a", "e": 1},
+            {"a": 1, "b": 1, "c": 1, "d": "a", "e": 1, "f": True},
             {"a": 2, "b": "a", "c": "a", "d": "a"},
             {"a": 3, "b": None, "c": 3, "d": "a", "e": 3},
         ]
-        expected = {"a": True, "b": False, "c": False, "d": False, "e": True}
+        expected = {"a": True, "b": False, "c": False, "d": False, "e": True, "f": False}
 
         trials = []
         for user_attrs in user_attrs_list: