diff --git a/.bumpversion.toml b/.bumpversion.toml
index 7ee8bec..0a15ce5 100644
--- a/.bumpversion.toml
+++ b/.bumpversion.toml
@@ -1,5 +1,5 @@
 [tool.bumpversion]
-current_version = "v0.4.0"
+current_version = "v0.4.1"
 commit = true
 commit_args = "--no-verify"
 tag = true
diff --git a/README.md b/README.md
index 89c5dbd..07e86fd 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,5 @@
 # totypes - Custom types for topology optimization
-`v0.4.0`
+`v0.4.1`
 
 ## Overview
 
diff --git a/pyproject.toml b/pyproject.toml
index 4dab19f..8505e87 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,7 +1,7 @@
 [project]
 
 name = "totypes"
-version = "v0.4.0"
+version = "v0.4.1"
 description = "Custom datatypes useful in a topology optimization context"
 keywords = ["topology", "optimization", "jax", "inverse design"]
 readme = "README.md"
diff --git a/src/totypes/__init__.py b/src/totypes/__init__.py
index a1572fe..0625a5b 100644
--- a/src/totypes/__init__.py
+++ b/src/totypes/__init__.py
@@ -3,7 +3,7 @@
 Copyright (c) 2023 The INVRS-IO authors.
 """
 
-__version__ = "v0.4.0"
+__version__ = "v0.4.1"
 __author__ = "Martin F. Schubert <mfschubert@gmail.com>"
 
 __all__ = ["json_utils", "symmetry", "types"]
diff --git a/src/totypes/json_utils.py b/src/totypes/json_utils.py
index ee3b01d..e393153 100644
--- a/src/totypes/json_utils.py
+++ b/src/totypes/json_utils.py
@@ -214,7 +214,7 @@ def _convert_array(arr: Union[onp.ndarray, jnp.ndarray]) -> Tuple[str, Dict[str,
 def _asdict(x: Any) -> Dict[str, Any]:
     """Converts dataclasses or namedtuples to dictionaries."""
     if dataclasses.is_dataclass(x):
-        return dataclasses.asdict(x)
+        return {field.name: getattr(x, field.name) for field in dataclasses.fields(x)}
     try:
         return x._asdict()  # type: ignore[no-any-return]
     except AttributeError as exc:
diff --git a/tests/test_json_utils.py b/tests/test_json_utils.py
index 2855e9d..fa0fa5f 100644
--- a/tests/test_json_utils.py
+++ b/tests/test_json_utils.py
@@ -222,6 +222,49 @@ class CustomObject(NamedTuple):
         self.assertEqual(restored.y, obj.y)
         self.assertEqual(restored.z, obj.z)
 
+    def test_serialize_with_custom_namedtuple_having_internal_custom_type(self):
+        class CustomObject(NamedTuple):
+            x: types.Density2DArray
+            y: types.BoundedArray
+            z: str
+
+        json_utils.register_custom_type(CustomObject)
+
+        obj = CustomObject(
+            x=types.Density2DArray(array=onp.zeros((5, 5))),
+            y=types.BoundedArray(onp.ones((3,)), 0, 2),
+            z="test",
+        )
+
+        serialized = json_utils.json_from_pytree(obj)
+        restored = json_utils.pytree_from_json(serialized)
+        self.assertIsInstance(restored, CustomObject)
+        self.assertIsInstance(restored.x, types.Density2DArray)
+        self.assertIsInstance(restored.y, types.BoundedArray)
+        self.assertIsInstance(restored.z, str)
+
+    def test_serialize_with_custom_dataclass_having_internal_custom_type(self):
+        @dataclasses.dataclass
+        class CustomObject:
+            x: types.Density2DArray
+            y: types.BoundedArray
+            z: str
+
+        json_utils.register_custom_type(CustomObject)
+
+        obj = CustomObject(
+            x=types.Density2DArray(array=onp.zeros((5, 5))),
+            y=types.BoundedArray(onp.ones((3,)), 0, 2),
+            z="test",
+        )
+
+        serialized = json_utils.json_from_pytree(obj)
+        restored = json_utils.pytree_from_json(serialized)
+        self.assertIsInstance(restored, CustomObject)
+        self.assertIsInstance(restored.x, types.Density2DArray)
+        self.assertIsInstance(restored.y, types.BoundedArray)
+        self.assertIsInstance(restored.z, str)
+
     def test_serialize_with_registered_custom_dataclass(self):
         @dataclasses.dataclass
         class CustomObject:
@@ -270,7 +313,6 @@ class MyClass123:
                 ["MyClass123" in key for key in json_utils._CUSTOM_TYPE_REGISTRY.keys()]
             )
         )
-        print(type(MyClass123()))
         with self.assertRaisesRegex(
             ValueError, "`custom_type` must be a type, but got"
         ):