diff --git a/src/aioice/ice.py b/src/aioice/ice.py
index f33a8dc..0eb99bd 100644
--- a/src/aioice/ice.py
+++ b/src/aioice/ice.py
@@ -865,7 +865,6 @@ async def get_component_candidates(
             except OSError as exc:
                 self.__log_info("Could not bind to %s - %s", address, exc)
                 continue
-            protocol = cast(StunProtocol, protocol)
             host_protocols.append(protocol)
 
             # add host candidate
@@ -911,7 +910,6 @@ async def get_component_candidates(
                 ssl=self.turn_ssl,
                 transport=self.turn_transport,
             )
-            protocol = cast(StunProtocol, protocol)
             self._protocols.append(protocol)
 
             # add relayed candidate
diff --git a/src/aioice/mdns.py b/src/aioice/mdns.py
index 2eac59e..7982a9c 100644
--- a/src/aioice/mdns.py
+++ b/src/aioice/mdns.py
@@ -189,4 +189,4 @@ async def create_mdns_protocol() -> MDnsProtocol:
         sock=rx_sock,
     )
 
-    return cast(MDnsProtocol, protocol)
+    return protocol
diff --git a/src/aioice/turn.py b/src/aioice/turn.py
index 360cf50..c54c9e6 100644
--- a/src/aioice/turn.py
+++ b/src/aioice/turn.py
@@ -4,7 +4,18 @@
 import socket
 import struct
 import time
-from typing import Any, Callable, Dict, List, Optional, Text, Tuple, Union, cast
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Text,
+    Tuple,
+    TypeVar,
+    Union,
+    cast,
+)
 
 from . import stun
 from .utils import random_transaction_id
@@ -17,6 +28,8 @@
 UDP_TRANSPORT = 0x11000000
 UDP_SOCKET_BUFFER_SIZE = 262144
 
+_ProtocolT = TypeVar("_ProtocolT", bound=asyncio.BaseProtocol)
+
 
 def is_channel_data(data: bytes) -> bool:
     return (data[0] & 0xC0) == 0x40
@@ -371,7 +384,7 @@ async def _connect(self) -> None:
 
 
 async def create_turn_endpoint(
-    protocol_factory: Callable,
+    protocol_factory: Callable[[], _ProtocolT],
     server_addr: Tuple[str, int],
     username: Optional[str],
     password: Optional[str],
@@ -379,11 +392,13 @@ async def create_turn_endpoint(
     channel_refresh_time: int = DEFAULT_CHANNEL_REFRESH_TIME,
     ssl: bool = False,
     transport: str = "udp",
-) -> Tuple[TurnTransport, asyncio.Protocol]:
+) -> Tuple[TurnTransport, _ProtocolT]:
     """
     Create datagram connection relayed over TURN.
     """
     loop = asyncio.get_event_loop()
+    inner_protocol: asyncio.BaseProtocol
+    inner_transport: asyncio.BaseTransport
     if transport == "tcp":
         inner_transport, inner_protocol = await loop.create_connection(
             lambda: TurnClientTcpProtocol(