diff --git a/serial_asyncio_fast/__init__.py b/serial_asyncio_fast/__init__.py
index f4c766f..54149e5 100644
--- a/serial_asyncio_fast/__init__.py
+++ b/serial_asyncio_fast/__init__.py
@@ -53,6 +53,10 @@ class SerialTransport(asyncio.Transport):
     calling you back when it succeeds.
     """
 
+    _loop: asyncio.AbstractEventLoop
+    _serial: serial.Serial
+    _protocol: asyncio.Protocol
+
     def __init__(
         self,
         loop: asyncio.AbstractEventLoop,
@@ -597,7 +601,7 @@ async def open_serial_connection(
     if loop is None:
         loop = asyncio.get_event_loop()
     if limit is None:
-        limit = asyncio.streams._DEFAULT_LIMIT
+        limit = 2 ** 16  # 64 KiB
     reader = asyncio.StreamReader(limit=limit, loop=loop)
     protocol = asyncio.StreamReaderProtocol(reader, loop=loop)
     transport, _ = await create_serial_connection(
@@ -612,9 +616,11 @@ async def open_serial_connection(
 if __name__ == "__main__":
 
     class Output(asyncio.Protocol):
+        
+        _transport: SerialTransport
+
         def __init__(self):
             super().__init__()
-            self._transport = None
 
         def connection_made(self, transport):
             self._transport = transport