diff --git a/src/async_wrapper/convert/_async.py b/src/async_wrapper/convert/_async.py
index cfc636f..3092c65 100644
--- a/src/async_wrapper/convert/_async.py
+++ b/src/async_wrapper/convert/_async.py
@@ -1,20 +1,20 @@
 from __future__ import annotations
 
 from functools import partial, wraps
-from typing import Any, Callable, Coroutine, TypeVar
+from typing import Any, Callable, Coroutine
 
 from anyio import to_thread
-from typing_extensions import ParamSpec
+from typing_extensions import ParamSpec, TypeVar
 
-ValueT_co = TypeVar("ValueT_co", covariant=True)
+ValueT = TypeVar("ValueT", infer_variance=True)
 ParamT = ParamSpec("ParamT")
 
 __all__ = ["sync_to_async"]
 
 
 def sync_to_async(
-    func: Callable[ParamT, ValueT_co],
-) -> Callable[ParamT, Coroutine[Any, Any, ValueT_co]]:
+    func: Callable[ParamT, ValueT],
+) -> Callable[ParamT, Coroutine[Any, Any, ValueT]]:
     """
     Convert a synchronous function to an asynchronous function.
 
@@ -55,7 +55,7 @@ def sync_to_async(
     """
 
     @wraps(func)
-    async def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT_co:
+    async def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT:
         return await to_thread.run_sync(partial(func, *args, **kwargs))
 
     return inner
diff --git a/src/async_wrapper/convert/_sync.py b/src/async_wrapper/convert/_sync.py
index 5e9d90a..7dc7a22 100644
--- a/src/async_wrapper/convert/_sync.py
+++ b/src/async_wrapper/convert/_sync.py
@@ -3,13 +3,13 @@
 from concurrent.futures import ThreadPoolExecutor, wait
 from contextvars import ContextVar
 from functools import partial, wraps
-from typing import Awaitable, Callable, TypeVar
+from typing import Awaitable, Callable
 
 import anyio
 from sniffio import AsyncLibraryNotFoundError, current_async_library
-from typing_extensions import ParamSpec
+from typing_extensions import ParamSpec, TypeVar
 
-ValueT_co = TypeVar("ValueT_co", covariant=True)
+ValueT = TypeVar("ValueT", infer_variance=True)
 ParamT = ParamSpec("ParamT")
 
 __all__ = ["async_to_sync"]
@@ -19,8 +19,8 @@
 
 
 def async_to_sync(
-    func: Callable[ParamT, Awaitable[ValueT_co]],
-) -> Callable[ParamT, ValueT_co]:
+    func: Callable[ParamT, Awaitable[ValueT]],
+) -> Callable[ParamT, ValueT]:
     """
     Convert an awaitable function to a synchronous function.
 
@@ -93,7 +93,7 @@ def async_to_sync(
     sync_func = _as_sync(func)
 
     @wraps(func)
-    def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT_co:
+    def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT:
         backend = _get_current_backend()
         use_uvloop = _check_uvloop()
         with ThreadPoolExecutor(
@@ -106,21 +106,19 @@ def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT_co:
     return inner
 
 
-def _as_sync(
-    func: Callable[ParamT, Awaitable[ValueT_co]],
-) -> Callable[ParamT, ValueT_co]:
+def _as_sync(func: Callable[ParamT, Awaitable[ValueT]]) -> Callable[ParamT, ValueT]:
     @wraps(func)
-    def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT_co:
+    def inner(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ValueT:
         return _run(func, *args, **kwargs)
 
     return inner
 
 
 def _run(
-    func: Callable[ParamT, Awaitable[ValueT_co]],
+    func: Callable[ParamT, Awaitable[ValueT]],
     *args: ParamT.args,
     **kwargs: ParamT.kwargs,
-) -> ValueT_co:
+) -> ValueT:
     backend = _get_current_backend()
     new_func = partial(func, *args, **kwargs)
     backend_options = {}
diff --git a/src/async_wrapper/convert/main.py b/src/async_wrapper/convert/main.py
index c6497b6..3bdf648 100644
--- a/src/async_wrapper/convert/main.py
+++ b/src/async_wrapper/convert/main.py
@@ -1,14 +1,14 @@
 from __future__ import annotations
 
 from inspect import iscoroutinefunction
-from typing import Any, Callable, Coroutine, TypeVar, overload
+from typing import Any, Callable, Coroutine, overload
 
-from typing_extensions import ParamSpec
+from typing_extensions import ParamSpec, TypeVar
 
 from ._async import sync_to_async
 from ._sync import async_to_sync
 
-ValueT = TypeVar("ValueT")
+ValueT = TypeVar("ValueT", infer_variance=True)
 ParamT = ParamSpec("ParamT")
 
 __all__ = ["toggle_func", "async_to_sync", "sync_to_async"]
diff --git a/src/async_wrapper/queue.py b/src/async_wrapper/queue.py
index 42aa447..43da1f1 100644
--- a/src/async_wrapper/queue.py
+++ b/src/async_wrapper/queue.py
@@ -13,12 +13,11 @@
     Generic,
     Literal,
     NoReturn,
-    TypeVar,
 )
 
 from anyio import WouldBlock, create_memory_object_stream, create_task_group, fail_after
 from anyio.streams.memory import BrokenResourceError, ClosedResourceError, EndOfStream
-from typing_extensions import override
+from typing_extensions import TypeVar, override
 
 from async_wrapper.exception import (
     QueueBrokenError,
@@ -43,8 +42,8 @@
 
 __all__ = ["Queue", "create_queue"]
 
-ValueT = TypeVar("ValueT")
-QueueT_co = TypeVar("QueueT_co", covariant=True, bound="Queue")
+ValueT = TypeVar("ValueT", infer_variance=True)
+QueueT = TypeVar("QueueT", infer_variance=True, bound="Queue")
 
 
 class Queue(Generic[ValueT]):
diff --git a/src/async_wrapper/task_group/task_group.py b/src/async_wrapper/task_group/task_group.py
index 2500b74..4d842f8 100644
--- a/src/async_wrapper/task_group/task_group.py
+++ b/src/async_wrapper/task_group/task_group.py
@@ -2,11 +2,11 @@
 
 from contextlib import AsyncExitStack
 from functools import partial, wraps
-from typing import TYPE_CHECKING, Any, Awaitable, Callable, Coroutine, Generic, TypeVar
+from typing import TYPE_CHECKING, Any, Awaitable, Callable, Coroutine, Generic
 
 from anyio import create_task_group as _create_task_group
 from anyio.abc import TaskGroup as _TaskGroup
-from typing_extensions import Concatenate, ParamSpec, Self, override
+from typing_extensions import Concatenate, ParamSpec, Self, TypeVar, override
 
 from async_wrapper.task_group.value import SoonValue
 
@@ -15,8 +15,8 @@
 
     from anyio.abc import CancelScope, CapacityLimiter, Lock, Semaphore
 
-ValueT_co = TypeVar("ValueT_co", covariant=True)
-OtherValueT_co = TypeVar("OtherValueT_co", covariant=True)
+ValueT = TypeVar("ValueT", infer_variance=True)
+OtherValueT = TypeVar("OtherValueT", infer_variance=True)
 ParamT = ParamSpec("ParamT")
 OtherParamT = ParamSpec("OtherParamT")
 
@@ -102,11 +102,11 @@ async def __aexit__(
 
     def wrap(
         self,
-        func: Callable[ParamT, Awaitable[ValueT_co]],
+        func: Callable[ParamT, Awaitable[ValueT]],
         semaphore: Semaphore | None = None,
         limiter: CapacityLimiter | None = None,
         lock: Lock | None = None,
-    ) -> SoonWrapper[ParamT, ValueT_co]:
+    ) -> SoonWrapper[ParamT, ValueT]:
         """
         Wrap a function to be used within a wrapper.
 
@@ -124,14 +124,14 @@ def wrap(
         return SoonWrapper(func, self, semaphore=semaphore, limiter=limiter, lock=lock)
 
 
-class SoonWrapper(Generic[ParamT, ValueT_co]):
+class SoonWrapper(Generic[ParamT, ValueT]):
     """wrapped func using in :class:`TaskGroupWrapper`"""
 
     __slots__ = ("func", "task_group", "semaphore", "limiter", "lock", "_wrapped")
 
     def __init__(  # noqa: PLR0913
         self,
-        func: Callable[ParamT, Awaitable[ValueT_co]],
+        func: Callable[ParamT, Awaitable[ValueT]],
         task_group: _TaskGroup,
         semaphore: Semaphore | None = None,
         limiter: CapacityLimiter | None = None,
@@ -147,8 +147,8 @@ def __init__(  # noqa: PLR0913
 
     def __call__(
         self, *args: ParamT.args, **kwargs: ParamT.kwargs
-    ) -> SoonValue[ValueT_co]:
-        value: SoonValue[ValueT_co] = SoonValue()
+    ) -> SoonValue[ValueT]:
+        value: SoonValue[ValueT] = SoonValue()
         wrapped = partial(self.wrapped, value, *args, **kwargs)
         self.task_group.start_soon(wrapped)
         return value
@@ -156,17 +156,15 @@ def __call__(
     @property
     def wrapped(
         self,
-    ) -> Callable[
-        Concatenate[SoonValue[ValueT_co], ParamT], Coroutine[Any, Any, ValueT_co]
-    ]:
+    ) -> Callable[Concatenate[SoonValue[ValueT], ParamT], Coroutine[Any, Any, ValueT]]:
         """wrapped func using semaphore"""
         if self._wrapped is not None:
             return self._wrapped
 
         @wraps(self.func)
         async def wrapped(
-            value: SoonValue[ValueT_co], *args: ParamT.args, **kwargs: ParamT.kwargs
-        ) -> ValueT_co:
+            value: SoonValue[ValueT], *args: ParamT.args, **kwargs: ParamT.kwargs
+        ) -> ValueT:
             async with AsyncExitStack() as stack:
                 if self.semaphore is not None:
                     await stack.enter_async_context(self.semaphore)
diff --git a/src/async_wrapper/task_group/value.py b/src/async_wrapper/task_group/value.py
index ea8ff1a..b552587 100644
--- a/src/async_wrapper/task_group/value.py
+++ b/src/async_wrapper/task_group/value.py
@@ -1,30 +1,32 @@
 from __future__ import annotations
 
 from threading import local
-from typing import Generic, TypeVar
+from typing import Generic
+
+from typing_extensions import TypeVar
 
 from async_wrapper.exception import PendingError
 
-ValueT_co = TypeVar("ValueT_co", covariant=True)
+ValueT = TypeVar("ValueT", infer_variance=True)
 Pending = local()
 
 __all__ = ["SoonValue"]
 
 
-class SoonValue(Generic[ValueT_co]):
+class SoonValue(Generic[ValueT]):
     """A class representing a value that will be available soon."""
 
     __slots__ = ("_value",)
 
     def __init__(self) -> None:
-        self._value: ValueT_co | local = Pending
+        self._value: ValueT | local = Pending
 
     def __repr__(self) -> str:
         status = "pending" if self._value is Pending else "done"
         return f"<SoonValue: status={status}>"
 
     @property
-    def value(self) -> ValueT_co:
+    def value(self) -> ValueT:
         """
         Gets the soon-to-be available value.
 
diff --git a/src/async_wrapper/wait.py b/src/async_wrapper/wait.py
index e5e6212..18ee7d4 100644
--- a/src/async_wrapper/wait.py
+++ b/src/async_wrapper/wait.py
@@ -2,10 +2,10 @@
 
 from functools import partial
 from threading import local
-from typing import TYPE_CHECKING, Any, Awaitable, Callable, Iterable, TypeVar
+from typing import TYPE_CHECKING, Any, Awaitable, Callable, Iterable
 
 from anyio import EndOfStream, Event, create_memory_object_stream, create_task_group
-from typing_extensions import ParamSpec, Self, override
+from typing_extensions import ParamSpec, Self, TypeVar, override
 
 from async_wrapper.exception import PendingError
 
@@ -19,7 +19,7 @@
 
 __all__ = ["Waiter", "Completed", "wait_for"]
 
-ValueT_co = TypeVar("ValueT_co", covariant=True)
+ValueT = TypeVar("ValueT", infer_variance=True)
 ParamT = ParamSpec("ParamT")
 Pending = local()
 
@@ -299,10 +299,10 @@ async def __anext__(self) -> Any:
 
 async def wait_for(
     event: Event | Iterable[Event],
-    func: Callable[ParamT, Awaitable[ValueT_co]],
+    func: Callable[ParamT, Awaitable[ValueT]],
     *args: ParamT.args,
     **kwargs: ParamT.kwargs,
-) -> ValueT_co:
+) -> ValueT:
     """
     Wait for an event before executing an awaitable function.