diff --git a/ably/transport/websockettransport.py b/ably/transport/websockettransport.py
index ad4f2856..cd048475 100644
--- a/ably/transport/websockettransport.py
+++ b/ably/transport/websockettransport.py
@@ -11,6 +11,7 @@
 import msgpack
 
 from ably.http.httputils import HttpUtils
+from ably.transport.defaults import Defaults
 from ably.types.connectiondetails import ConnectionDetails
 from ably.types.operations import PublishResult
 from ably.util.eventemitter import EventEmitter
@@ -81,7 +82,8 @@ def connect(self):
         headers = HttpUtils.default_headers()
         query_params = urllib.parse.urlencode(self.params)
         scheme = 'wss' if self.options.tls else 'ws'
-        ws_url = f'{scheme}://{self.host}?{query_params}'
+        port = Defaults.get_port(self.options)
+        ws_url = f'{scheme}://{self.host}:{port}?{query_params}'
         log.info(f'connect(): attempting to connect to {ws_url}')
         self.ws_connect_task = asyncio.create_task(self.ws_connect(ws_url, headers))
         self.ws_connect_task.add_done_callback(self.on_ws_connect_done)
diff --git a/test/ably/realtime/realtimeconnection_test.py b/test/ably/realtime/realtimeconnection_test.py
index dbd20698..d187a378 100644
--- a/test/ably/realtime/realtimeconnection_test.py
+++ b/test/ably/realtime/realtimeconnection_test.py
@@ -67,8 +67,8 @@ async def close_active_connection(self):
 
     @property
     def endpoint(self) -> str:
-        """Endpoint string to pass to AblyRealtime (combine with tls=False)."""
-        return f"127.0.0.1:{self.port}"
+        """Host to pass to AblyRealtime (combine with tls=False and port=self.port)."""
+        return "127.0.0.1"
 
     async def __aenter__(self):
         self.server = await ws_serve(self._handler, "127.0.0.1", 0, ping_interval=None)
@@ -242,6 +242,7 @@ async def test_ping_survives_connection_drop(self):
                 realtime_request_timeout=20000,
                 tls=False,
                 endpoint=proxy.endpoint,
+                port=proxy.port,
             )
             try:
                 await asyncio.wait_for(ably.connection.once_async(ConnectionState.CONNECTED), timeout=10)
@@ -654,6 +655,7 @@ async def test_normal_ws_close_triggers_immediate_reconnection(self):
                 suspended_retry_timeout=500_000,
                 tls=False,
                 endpoint=proxy.endpoint,
+                port=proxy.port,
             )
 
             try:
diff --git a/test/unit/websockettransport_test.py b/test/unit/websockettransport_test.py
new file mode 100644
index 00000000..d45c3ca8
--- /dev/null
+++ b/test/unit/websockettransport_test.py
@@ -0,0 +1,39 @@
+from unittest.mock import MagicMock, patch
+
+from ably.transport.websockettransport import WebSocketTransport
+from ably.types.options import Options
+
+
+def _connect_url(host='example.com', **option_kwargs):
+    connection_manager = MagicMock()
+    connection_manager.options = Options(auth_token='foo', **option_kwargs)
+    transport = WebSocketTransport(connection_manager, host, {'format': 'json'})
+    with patch.object(transport, 'ws_connect', MagicMock()) as mock_ws_connect:
+        with patch('ably.transport.websockettransport.asyncio.create_task') as mock_create_task:
+            mock_create_task.return_value = MagicMock()
+            transport.connect()
+    return mock_ws_connect.call_args[0][0]
+
+
+# TO3d, TO3o
+def test_websocket_url_uses_wss_and_tls_port_when_tls_enabled():
+    url = _connect_url(tls=True, tls_port=9999)
+    assert url == 'wss://example.com:9999?format=json'
+
+
+# TO3d, TO3n
+def test_websocket_url_uses_ws_and_port_when_tls_disabled():
+    url = _connect_url(tls=False, port=9998)
+    assert url == 'ws://example.com:9998?format=json'
+
+
+# TO3d, TO3o
+def test_websocket_url_defaults_to_wss_and_443():
+    url = _connect_url()
+    assert url == 'wss://example.com:443?format=json'
+
+
+# TO3d, TO3n
+def test_websocket_url_defaults_to_ws_and_80_when_tls_disabled():
+    url = _connect_url(tls=False)
+    assert url == 'ws://example.com:80?format=json'