diff --git a/stdlib/asyncio/streams.pyi b/stdlib/asyncio/streams.pyi
index 4dff8d28b..c3cc7b8c9 100644
--- a/stdlib/asyncio/streams.pyi
+++ b/stdlib/asyncio/streams.pyi
@@ -1,8 +1,8 @@
 import ssl
 import sys
-from _typeshed import StrPath
-from collections.abc import AsyncIterator, Awaitable, Callable, Iterable, Sequence
-from typing import Any, SupportsIndex
+from _typeshed import ReadableBuffer, StrPath
+from collections.abc import AsyncIterator, Awaitable, Callable, Iterable, Sequence, Sized
+from typing import Any, Protocol, SupportsIndex
 from typing_extensions import Self, TypeAlias
 
 from . import events, protocols, transports
@@ -23,6 +23,8 @@ else:
 
 _ClientConnectedCallback: TypeAlias = Callable[[StreamReader, StreamWriter], Awaitable[None] | None]
 
+class _ReaduntilBuffer(ReadableBuffer, Sized, Protocol): ...
+
 if sys.version_info >= (3, 10):
     async def open_connection(
         host: str | None = None,
@@ -140,8 +142,11 @@ class StreamReader(AsyncIterator[bytes]):
     def at_eof(self) -> bool: ...
     def feed_data(self, data: Iterable[SupportsIndex]) -> None: ...
     async def readline(self) -> bytes: ...
-    # Can be any buffer that supports len(); consider changing to a Protocol if PEP 688 is accepted
-    async def readuntil(self, separator: bytes | bytearray | memoryview = b"\n") -> bytes: ...
+    if sys.version_info >= (3, 13):
+        async def readuntil(self, separator: _ReaduntilBuffer | tuple[_ReaduntilBuffer, ...] = b"\n") -> bytes: ...
+    else:
+        async def readuntil(self, separator: _ReaduntilBuffer = b"\n") -> bytes: ...
+
     async def read(self, n: int = -1) -> bytes: ...
     async def readexactly(self, n: int) -> bytes: ...
     def __aiter__(self) -> Self: ...