diff --git a/src/snakia/field/auto.py b/src/snakia/field/auto.py
index 12e7d25..f456a1d 100644
--- a/src/snakia/field/auto.py
+++ b/src/snakia/field/auto.py
@@ -3,6 +3,8 @@ from typing import Callable, Final, Generic, TypeVar, overload
 
 from typing_extensions import Self
 
+from snakia.types import Unset
+
 from .field import Field
 
 T = TypeVar("T")
@@ -13,33 +15,38 @@ class AutoField(Field[T], Generic[T]):
 
     @overload
     def __init__(
-        self, default_value: T, *, target_type: type[T] | None = None
+        self, default_value: T, *, target_type: type[T] | Unset = Unset()
     ) -> None: ...
+
     @overload
     def __init__(
         self,
         *,
         default_factory: Callable[[Self], T],
-        target_type: type[T] | None = None,
+        target_type: type[T] | Unset = Unset(),
     ) -> None: ...
+
     def __init__(
         self,
-        default_value: T | None = None,
+        default_value: T | Unset = Unset(),
         *,
-        default_factory: Callable[[Self], T] | None = None,
-        target_type: type[T] | None = None,
+        default_factory: Callable[[Self], T] | Unset = Unset(),
+        target_type: type[T] | Unset = Unset(),
     ) -> None:
-        if default_factory is not None and default_value is None:
-            super().__init__(default_factory=default_factory)
-        elif default_value is not None and default_factory is None:
-            super().__init__(default_value)
-        self.__target_type: Final = target_type
+        if not Unset.itis(default_factory):
+            super().__init__(default_factory=Unset.unwrap(default_factory))
+        elif not Unset.itis(default_value):
+            super().__init__(Unset.unwrap(default_value))
+        else:
+            super().__init__()
+        self.__target_type: Final[type] = Unset.unwrap_or(target_type, object)
 
     def serialize(self, value: T, /) -> bytes:
         return pickle.dumps(value)
 
     def deserialize(self, serialized: bytes, /) -> T:
         value = pickle.loads(serialized)
-        if not isinstance(value, self.__target_type or object):
+        
+        if not isinstance(value, self.__target_type):
             return self._get_default()
         return value  # type: ignore
diff --git a/src/snakia/property/priv_property.py b/src/snakia/property/priv_property.py
index 705a2e6..fba63da 100644
--- a/src/snakia/property/priv_property.py
+++ b/src/snakia/property/priv_property.py
@@ -1,6 +1,9 @@
 from typing import Any, Callable, Final, Generic, TypeVar, overload
+
 from typing_extensions import Self
 
+from snakia.types import Unset
+
 T = TypeVar("T")
 
 
@@ -17,20 +20,18 @@ class PrivProperty(Generic[T]):
     def __init__(self, *, default_factory: Callable[[Self], T]) -> None: ...
     def __init__(
         self,
-        default_value: T | None = None,
-        default_factory: Callable[[Self], T] | None = None,
+        default_value: T | Unset = Unset(),
+        default_factory: Callable[[Self], T] | Unset = Unset(),
     ) -> None:
-        self.__default_value: Final[T | None] = default_value
-        self.__default_factory: Final[Callable[[Self], T] | None] = (
-            default_factory
-        )
+        self.__default_value: Final[T | Unset] = default_value
+        self.__default_factory: Final[Callable[[Self], T] | Unset] = default_factory
 
     def _get_default(self: Self) -> T:
-        if self.__default_value is not None:
-            return self.__default_value
-        if self.__default_factory is not None:
-            return self.__default_factory(self)
-        raise ValueError("Either default_value or default_factory must be set")
+        return Unset.map(
+            self.__default_factory,
+            lambda f: f(self),
+            lambda _: Unset.unwrap(self.__default_value),
+        )
 
     def __set_name__(self, owner: type, name: str) -> None:
         self.__name = f"_{owner.__name__}__{name}"