diff --git a/mashumaro/core/meta/helpers.py b/mashumaro/core/meta/helpers.py
index ea0188c2..891c1e61 100644
--- a/mashumaro/core/meta/helpers.py
+++ b/mashumaro/core/meta/helpers.py
@@ -272,8 +272,9 @@ def type_name(
             )
             return f"{_typing_name('Union', short)}[{args_str}]"
         else:
-            bound = getattr(typ, "__default__", None)
-            if bound is None:
+            if type_var_has_default(typ):
+                bound = get_type_var_default(typ)
+            else:
                 bound = getattr(typ, "__bound__")
             return type_name(bound, short, resolved_type_params)
     elif is_new_type(typ) and not PY_310_MIN:
@@ -423,7 +424,7 @@ def is_type_var_any(typ: Type) -> bool:
         return False
     elif typ.__bound__ not in (None, Any):
         return False
-    elif getattr(typ, "__default__", None) not in (None, NoneType):
+    elif type_var_has_default(typ):
         return False
     else:
         return True
@@ -806,3 +807,14 @@ def is_type_alias_type(typ: Type) -> bool:
         return isinstance(typ, typing.TypeAliasType)  # type: ignore
     else:
         return False
+
+
+def type_var_has_default(typ: Any) -> bool:
+    try:
+        return typ.has_default()
+    except AttributeError:
+        return getattr(typ, "__default__", None) is not None
+
+
+def get_type_var_default(typ: Any) -> Type:
+    return getattr(typ, "__default__")
diff --git a/mashumaro/core/meta/types/pack.py b/mashumaro/core/meta/types/pack.py
index e8b46371..db8a09cb 100644
--- a/mashumaro/core/meta/types/pack.py
+++ b/mashumaro/core/meta/types/pack.py
@@ -31,6 +31,7 @@
     get_function_return_annotation,
     get_literal_values,
     get_type_origin,
+    get_type_var_default,
     is_final,
     is_generic,
     is_literal,
@@ -52,6 +53,7 @@
     resolve_type_params,
     substitute_type_params,
     type_name,
+    type_var_has_default,
 )
 from mashumaro.core.meta.types.common import (
     Expression,
@@ -471,8 +473,9 @@ def pack_special_typing_primitive(spec: ValueSpec) -> Optional[Expression]:
             if constraints:
                 return pack_union(spec, constraints, "type_var")
             else:
-                bound = getattr(spec.type, "__default__", None)
-                if bound is None:
+                if type_var_has_default(spec.type):
+                    bound = get_type_var_default(spec.type)
+                else:
                     bound = getattr(spec.type, "__bound__")
                 # act as if it was Optional[bound]
                 pv = PackerRegistry.get(spec.copy(type=bound))
diff --git a/mashumaro/core/meta/types/unpack.py b/mashumaro/core/meta/types/unpack.py
index 78e14b6f..15bf1ac0 100644
--- a/mashumaro/core/meta/types/unpack.py
+++ b/mashumaro/core/meta/types/unpack.py
@@ -37,6 +37,7 @@
     get_class_that_defines_method,
     get_function_arg_annotation,
     get_literal_values,
+    get_type_var_default,
     is_final,
     is_generic,
     is_literal,
@@ -59,6 +60,7 @@
     resolve_type_params,
     substitute_type_params,
     type_name,
+    type_var_has_default,
 )
 from mashumaro.core.meta.types.common import (
     AbstractMethodBuilder,
@@ -749,8 +751,9 @@ def unpack_special_typing_primitive(spec: ValueSpec) -> Optional[Expression]:
             if constraints:
                 return TypeVarUnpackerBuilder(constraints).build(spec)
             else:
-                bound = getattr(spec.type, "__default__", None)
-                if bound is None:
+                if type_var_has_default(spec.type):
+                    bound = get_type_var_default(spec.type)
+                else:
                     bound = getattr(spec.type, "__bound__")
                 # act as if it was Optional[bound]
                 uv = UnpackerRegistry.get(spec.copy(type=bound))
diff --git a/tests/test_meta.py b/tests/test_meta.py
index e50cb08a..09be6ca3 100644
--- a/tests/test_meta.py
+++ b/tests/test_meta.py
@@ -29,6 +29,7 @@
     get_literal_values,
     get_type_annotations,
     get_type_origin,
+    get_type_var_default,
     hash_type_args,
     is_annotated,
     is_dataclass_dict_mixin,
@@ -49,6 +50,7 @@
     resolve_type_params,
     substitute_type_params,
     type_name,
+    type_var_has_default,
 )
 from mashumaro.core.meta.types.common import (
     FieldContext,
@@ -807,3 +809,25 @@ def test_is_hashable_type():
     assert is_hashable_type(int) is True
     assert is_hashable_type(MyFrozenDataClass) is True
     assert is_hashable_type(MyDataClass) is False
+
+
+def test_type_var_has_default():
+    T_WithoutDefault = typing_extensions.TypeVar("T_WithoutDefault")
+    T_WithDefault = typing_extensions.TypeVar("T_WithDefault", default=int)
+    T_WithDefaultNone = typing_extensions.TypeVar(
+        "T_WithDefaultNone", default=None
+    )
+
+    assert not type_var_has_default(T_WithoutDefault)
+    assert type_var_has_default(T_WithDefault)
+    assert type_var_has_default(T_WithDefaultNone)
+
+
+def test_get_type_var_default():
+    T_WithDefault = typing_extensions.TypeVar("T_WithDefault", default=int)
+    T_WithDefaultNone = typing_extensions.TypeVar(
+        "T_WithDefaultNone", default=None
+    )
+
+    assert get_type_var_default(T_WithDefault) is int
+    assert get_type_var_default(T_WithDefaultNone) is None