diff --git a/flexeval/core/utils/json_util.py b/flexeval/core/utils/json_util.py
index e47e6586..451312fc 100644
--- a/flexeval/core/utils/json_util.py
+++ b/flexeval/core/utils/json_util.py
@@ -13,6 +13,8 @@ def _truncate_base64(o: Any) -> Any:  # noqa: ANN401
         return type(o)(_truncate_base64(item) for item in o)
     if isinstance(o, dict):
         return {k: _truncate_base64(v) for k, v in o.items()}
+    if isinstance(o, (int, float, bool, type(None))):
+        return o
 
     s = str(o)
 
diff --git a/tests/core/utils/test_json_util.py b/tests/core/utils/test_json_util.py
index 42f460c9..32af4574 100644
--- a/tests/core/utils/test_json_util.py
+++ b/tests/core/utils/test_json_util.py
@@ -1,6 +1,7 @@
 import dataclasses
 import json
-from ast import literal_eval
+
+import pytest
 
 from flexeval.core.utils.json_util import Base64TruncatingJSONEncoder
 
@@ -8,7 +9,7 @@
 @dataclasses.dataclass
 class TestDataClass:
     field1: str
-    field2: int
+    field2: int | float | bool | None
 
 
 class TestData:
@@ -27,25 +28,32 @@ def test_truncate_base64() -> None:
     def _json_dumps(x):  # noqa: ANN001, ANN202
         return json.dumps(x, cls=Base64TruncatingJSONEncoder)
 
-    assert literal_eval(_json_dumps(TestDataClass("example", 123))) == {"field1": "example", "field2": "123"}
+    assert json.loads(_json_dumps(TestDataClass("example", 123))) == {"field1": "example", "field2": 123}
+
+    assert json.loads(_json_dumps(TestDataClass("example", 1.23))) == pytest.approx(
+        {"field1": "example", "field2": 1.23}
+    )
+
+    assert json.loads(_json_dumps(TestDataClass("example", True))) == {"field1": "example", "field2": True}
+    assert json.loads(_json_dumps(TestDataClass("example", None))) == {"field1": "example", "field2": None}
 
-    assert literal_eval(_json_dumps(TestData())) == "TestData"
+    assert json.loads(_json_dumps(TestData())) == "TestData"
 
-    assert literal_eval(_json_dumps({"key": base64_string})) == {
+    assert json.loads(_json_dumps({"key": base64_string})) == {
         "key": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAgA/... [truncated, 169 chars total]"
     }
 
-    assert literal_eval(_json_dumps([base64_string, "normal string"])) == [
+    assert json.loads(_json_dumps([base64_string, "normal string"])) == [
         "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAgA/... [truncated, 169 chars total]",
         "normal string",
     ]
 
-    assert literal_eval(_json_dumps(TestDataClass(base64_string, 456))) == {
+    assert json.loads(_json_dumps(TestDataClass(base64_string, 456))) == {
         "field1": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAgA/... [truncated, 169 chars total]",
-        "field2": "456",
+        "field2": 456,
     }
 
-    image_url = literal_eval(
+    image_url = json.loads(
         _json_dumps({"messages": [{"content": {"type": "image_url", "image_url": {"url": base64_string}}}]})
     )
     assert (