diff --git a/src/socketio/async_aiopika_manager.py b/src/socketio/async_aiopika_manager.py
index 34171c46..626158bf 100644
--- a/src/socketio/async_aiopika_manager.py
+++ b/src/socketio/async_aiopika_manager.py
@@ -1,6 +1,5 @@
 import asyncio
 
-from engineio import json
 from .async_pubsub_manager import AsyncPubSubManager
 
 try:
@@ -32,18 +31,29 @@ class AsyncAioPikaManager(AsyncPubSubManager):  # pragma: no cover
                     in rabbitmq
     :param write_only: If set to ``True``, only initialize to emit events. The
                        default of ``False`` initializes the class for emitting
-                       and receiving.
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     """
 
     name = 'asyncaiopika'
 
     def __init__(self, url='amqp://guest:guest@localhost:5672//',
-                 channel='socketio', write_only=False, logger=None):
+                 channel='socketio', write_only=False, logger=None, json=None):
         if aio_pika is None:
             raise RuntimeError('aio_pika package is not installed '
                                '(Run "pip install aio_pika" in your '
                                'virtualenv).')
-        super().__init__(channel=channel, write_only=write_only, logger=logger)
+        super().__init__(channel=channel, write_only=write_only, logger=logger,
+                         json=json)
         self.url = url
         self._lock = asyncio.Lock()
         self.publisher_connection = None
@@ -82,7 +92,7 @@ async def _publish(self, data):
             try:
                 await self.publisher_exchange.publish(
                     aio_pika.Message(
-                        body=json.dumps(data).encode(),
+                        body=self.json.dumps(data).encode(),
                         delivery_mode=aio_pika.DeliveryMode.PERSISTENT
                     ), routing_key='*',
                 )
diff --git a/src/socketio/async_client.py b/src/socketio/async_client.py
index 49241ed0..cdbcc1b6 100644
--- a/src/socketio/async_client.py
+++ b/src/socketio/async_client.py
@@ -37,10 +37,11 @@ class AsyncClient(base_client.BaseClient):
                    use. To disable logging set to ``False``. The default is
                    ``False``. Note that fatal errors are logged even when
                    ``logger`` is ``False``.
-    :param json: An alternative json module to use for encoding and decoding
+    :param json: An alternative JSON module to use for encoding and decoding
                  packets. Custom json modules must have ``dumps`` and ``loads``
                  functions that are compatible with the standard library
-                 versions.
+                 versions. This is a process-wide setting, all instantiated
+                 servers and clients must use the same JSON module.
     :param handle_sigint: Set to ``True`` to automatically handle disconnection
                           when the process is interrupted, or to ``False`` to
                           leave interrupt handling to the calling application.
diff --git a/src/socketio/async_pubsub_manager.py b/src/socketio/async_pubsub_manager.py
index 6d631640..b29e521d 100644
--- a/src/socketio/async_pubsub_manager.py
+++ b/src/socketio/async_pubsub_manager.py
@@ -3,8 +3,6 @@
 from functools import partial
 import uuid
 
-from engineio import json
-
 from .async_manager import AsyncManager
 from .packet import Packet
 
@@ -22,15 +20,31 @@ class AsyncPubSubManager(AsyncManager):
 
     :param channel: The channel name on which the server sends and receives
                     notifications.
+    :param write_only: If set to ``True``, only initialize to emit events. The
+                       default of ``False`` initializes the class for emitting
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     """
     name = 'asyncpubsub'
 
-    def __init__(self, channel='socketio', write_only=False, logger=None):
+    def __init__(self, channel='socketio', write_only=False, logger=None,
+                 json=None):
         super().__init__()
         self.channel = channel
         self.write_only = write_only
         self.host_id = uuid.uuid4().hex
         self.logger = logger
+        if json is not None:
+            self.json = json
 
     def initialize(self):
         super().initialize()
@@ -221,7 +235,7 @@ async def _thread(self):
                         data = message
                     else:
                         try:
-                            data = json.loads(message)
+                            data = self.json.loads(message)
                         except:
                             pass
                     if data and 'method' in data:
diff --git a/src/socketio/async_redis_manager.py b/src/socketio/async_redis_manager.py
index a43807ca..862e6104 100644
--- a/src/socketio/async_redis_manager.py
+++ b/src/socketio/async_redis_manager.py
@@ -19,7 +19,6 @@
     aiovalkey = None
     ValkeyError = None
 
-from engineio import json
 from .async_pubsub_manager import AsyncPubSubManager
 from .redis_manager import parse_redis_sentinel_url
 
@@ -47,18 +46,29 @@ class AsyncRedisManager(AsyncPubSubManager):
                     notifications. Must be the same in all the servers.
     :param write_only: If set to ``True``, only initialize to emit events. The
                        default of ``False`` initializes the class for emitting
-                       and receiving.
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     :param redis_options: additional keyword arguments to be passed to
                           ``Redis.from_url()`` or ``Sentinel()``.
     """
     name = 'aioredis'
 
     def __init__(self, url='redis://localhost:6379/0', channel='socketio',
-                 write_only=False, logger=None, redis_options=None):
+                 write_only=False, logger=None, json=None, redis_options=None):
         if aioredis and \
                 not hasattr(aioredis.Redis, 'from_url'):  # pragma: no cover
             raise RuntimeError('Version 2 of aioredis package is required.')
-        super().__init__(channel=channel, write_only=write_only, logger=logger)
+        super().__init__(channel=channel, write_only=write_only, logger=logger,
+                         json=json)
         self.redis_url = url
         self.redis_options = redis_options or {}
         self.connected = False
@@ -117,7 +127,7 @@ async def _publish(self, data):  # pragma: no cover
                 if not self.connected:
                     self._redis_connect()
                 return await self.redis.publish(
-                    self.channel, json.dumps(data))
+                    self.channel, self.json.dumps(data))
             except error as exc:
                 if retries_left > 0:
                     self._get_logger().error(
diff --git a/src/socketio/async_server.py b/src/socketio/async_server.py
index e13009ef..733d6e94 100644
--- a/src/socketio/async_server.py
+++ b/src/socketio/async_server.py
@@ -28,10 +28,11 @@ class AsyncServer(base_server.BaseServer):
     :param logger: To enable logging set to ``True`` or pass a logger object to
                    use. To disable logging set to ``False``. Note that fatal
                    errors are logged even when ``logger`` is ``False``.
-    :param json: An alternative json module to use for encoding and decoding
+    :param json: An alternative JSON module to use for encoding and decoding
                  packets. Custom json modules must have ``dumps`` and ``loads``
                  functions that are compatible with the standard library
-                 versions.
+                 versions. This is a process-wide setting, all instantiated
+                 servers and clients must use the same JSON module.
     :param async_handlers: If set to ``True``, event handlers for a client are
                            executed in separate threads. To run handlers for a
                            client synchronously, set to ``False``. The default
diff --git a/src/socketio/base_manager.py b/src/socketio/base_manager.py
index ae4530bd..7b092ead 100644
--- a/src/socketio/base_manager.py
+++ b/src/socketio/base_manager.py
@@ -1,5 +1,6 @@
 import itertools
 import logging
+import json
 
 from bidict import bidict, ValueDuplicationError
 
@@ -14,9 +15,11 @@ def __init__(self):
         self.eio_to_sid = {}
         self.callbacks = {}
         self.pending_disconnect = {}
+        self.json = json
 
     def set_server(self, server):
         self.server = server
+        self.json = self.server.packet_class.json  # use the global JSON module
 
     def initialize(self):
         """Invoked before the first request is received. Subclasses can add
diff --git a/src/socketio/client.py b/src/socketio/client.py
index 5282e0a1..8f38316e 100644
--- a/src/socketio/client.py
+++ b/src/socketio/client.py
@@ -39,10 +39,11 @@ class Client(base_client.BaseClient):
                        of the ``encode()`` and ``decode()`` methods can be
                        provided. Client and server must use compatible
                        serializers.
-    :param json: An alternative json module to use for encoding and decoding
+    :param json: An alternative JSON module to use for encoding and decoding
                  packets. Custom json modules must have ``dumps`` and ``loads``
                  functions that are compatible with the standard library
-                 versions.
+                 versions. This is a process-wide setting, all instantiated
+                 servers and clients must use the same JSON module.
     :param handle_sigint: Set to ``True`` to automatically handle disconnection
                           when the process is interrupted, or to ``False`` to
                           leave interrupt handling to the calling application.
diff --git a/src/socketio/kafka_manager.py b/src/socketio/kafka_manager.py
index a9f1a075..afa28ff9 100644
--- a/src/socketio/kafka_manager.py
+++ b/src/socketio/kafka_manager.py
@@ -5,7 +5,6 @@
 except ImportError:
     kafka = None
 
-from engineio import json
 from .pubsub_manager import PubSubManager
 
 logger = logging.getLogger('socketio')
@@ -32,18 +31,29 @@ class KafkaManager(PubSubManager):  # pragma: no cover
                     servers.
     :param write_only: If set to ``True``, only initialize to emit events. The
                        default of ``False`` initializes the class for emitting
-                       and receiving.
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     """
     name = 'kafka'
 
     def __init__(self, url='kafka://localhost:9092', channel='socketio',
-                 write_only=False):
+                 write_only=False, logger=None, json=None):
         if kafka is None:
             raise RuntimeError('kafka-python package is not installed '
                                '(Run "pip install kafka-python" in your '
                                'virtualenv).')
 
-        super().__init__(channel=channel, write_only=write_only)
+        super().__init__(channel=channel, write_only=write_only, logger=logger,
+                         json=json)
 
         urls = [url] if isinstance(url, str) else url
         self.kafka_urls = [url[8:] if url != 'kafka://' else 'localhost:9092'
@@ -53,7 +63,7 @@ def __init__(self, url='kafka://localhost:9092', channel='socketio',
                                             bootstrap_servers=self.kafka_urls)
 
     def _publish(self, data):
-        self.producer.send(self.channel, value=json.dumps(data))
+        self.producer.send(self.channel, value=self.json.dumps(data))
         self.producer.flush()
 
     def _kafka_listen(self):
diff --git a/src/socketio/kombu_manager.py b/src/socketio/kombu_manager.py
index ae9d1393..d17505e8 100644
--- a/src/socketio/kombu_manager.py
+++ b/src/socketio/kombu_manager.py
@@ -6,7 +6,6 @@
 except ImportError:
     kombu = None
 
-from engineio import json
 from .pubsub_manager import PubSubManager
 
 
@@ -34,7 +33,17 @@ class KombuManager(PubSubManager):  # pragma: no cover
                     notifications. Must be the same in all the servers.
     :param write_only: If set to ``True``, only initialize to emit events. The
                        default of ``False`` initializes the class for emitting
-                       and receiving.
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     :param connection_options: additional keyword arguments to be passed to
                                ``kombu.Connection()``.
     :param exchange_options: additional keyword arguments to be passed to
@@ -47,14 +56,15 @@ class KombuManager(PubSubManager):  # pragma: no cover
     name = 'kombu'
 
     def __init__(self, url='amqp://guest:guest@localhost:5672//',
-                 channel='socketio', write_only=False, logger=None,
+                 channel='socketio', write_only=False, logger=None, json=None,
                  connection_options=None, exchange_options=None,
                  queue_options=None, producer_options=None):
         if kombu is None:
             raise RuntimeError('Kombu package is not installed '
                                '(Run "pip install kombu" in your '
                                'virtualenv).')
-        super().__init__(channel=channel, write_only=write_only, logger=logger)
+        super().__init__(channel=channel, write_only=write_only, logger=logger,
+                         json=json)
         self.url = url
         self.connection_options = connection_options or {}
         self.exchange_options = exchange_options or {}
@@ -102,7 +112,7 @@ def _publish(self, data):
             try:
                 producer_publish = self._producer_publish(
                     self.publisher_connection)
-                producer_publish(json.dumps(data))
+                producer_publish(self.json.dumps(data))
                 break
             except (OSError, kombu.exceptions.KombuError):
                 if retry:
diff --git a/src/socketio/pubsub_manager.py b/src/socketio/pubsub_manager.py
index 4254d4af..9a77e3f6 100644
--- a/src/socketio/pubsub_manager.py
+++ b/src/socketio/pubsub_manager.py
@@ -2,8 +2,6 @@
 from functools import partial
 import uuid
 
-from engineio import json
-
 from .manager import Manager
 from .packet import Packet
 
@@ -21,15 +19,31 @@ class PubSubManager(Manager):
 
     :param channel: The channel name on which the server sends and receives
                     notifications.
+    :param write_only: If set to ``True``, only initialize to emit events. The
+                       default of ``False`` initializes the class for emitting
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     """
     name = 'pubsub'
 
-    def __init__(self, channel='socketio', write_only=False, logger=None):
+    def __init__(self, channel='socketio', write_only=False, logger=None,
+                 json=None):
         super().__init__()
         self.channel = channel
         self.write_only = write_only
         self.host_id = uuid.uuid4().hex
         self.logger = logger
+        if json is not None:
+            self.json = json
 
     def initialize(self):
         super().initialize()
@@ -215,7 +229,7 @@ def _thread(self):
                         data = message
                     else:
                         try:
-                            data = json.loads(message)
+                            data = self.json.loads(message)
                         except:
                             pass
                     if data and 'method' in data:
diff --git a/src/socketio/redis_manager.py b/src/socketio/redis_manager.py
index 4a9d69d1..fb2e0400 100644
--- a/src/socketio/redis_manager.py
+++ b/src/socketio/redis_manager.py
@@ -16,7 +16,6 @@
     valkey = None
     ValkeyError = None
 
-from engineio import json
 from .pubsub_manager import PubSubManager
 
 logger = logging.getLogger('socketio')
@@ -72,15 +71,26 @@ class RedisManager(PubSubManager):
                     notifications. Must be the same in all the servers.
     :param write_only: If set to ``True``, only initialize to emit events. The
                        default of ``False`` initializes the class for emitting
-                       and receiving.
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
     :param redis_options: additional keyword arguments to be passed to
                           ``Redis.from_url()`` or ``Sentinel()``.
     """
     name = 'redis'
 
     def __init__(self, url='redis://localhost:6379/0', channel='socketio',
-                 write_only=False, logger=None, redis_options=None):
-        super().__init__(channel=channel, write_only=write_only, logger=logger)
+                 write_only=False, logger=None, json=None, redis_options=None):
+        super().__init__(channel=channel, write_only=write_only, logger=logger,
+                         json=json)
         self.redis_url = url
         self.redis_options = redis_options or {}
         self.connected = False
@@ -153,7 +163,7 @@ def _publish(self, data):  # pragma: no cover
             try:
                 if not self.connected:
                     self._redis_connect()
-                return self.redis.publish(self.channel, json.dumps(data))
+                return self.redis.publish(self.channel, self.json.dumps(data))
             except error as exc:
                 if retries_left > 0:
                     logger.error(
diff --git a/src/socketio/server.py b/src/socketio/server.py
index f3257081..6a1a2026 100644
--- a/src/socketio/server.py
+++ b/src/socketio/server.py
@@ -30,10 +30,11 @@ class Server(base_server.BaseServer):
                        of the ``encode()`` and ``decode()`` methods can be
                        provided. Client and server must use compatible
                        serializers.
-    :param json: An alternative json module to use for encoding and decoding
+    :param json: An alternative JSON module to use for encoding and decoding
                  packets. Custom json modules must have ``dumps`` and ``loads``
                  functions that are compatible with the standard library
-                 versions.
+                 versions. This is a process-wide setting, all instantiated
+                 servers and clients must use the same JSON module.
     :param async_handlers: If set to ``True``, event handlers for a client are
                            executed in separate threads. To run handlers for a
                            client synchronously, set to ``False``. The default
diff --git a/src/socketio/zmq_manager.py b/src/socketio/zmq_manager.py
index a71b869c..3fa1e145 100644
--- a/src/socketio/zmq_manager.py
+++ b/src/socketio/zmq_manager.py
@@ -1,6 +1,5 @@
 import re
 
-from engineio import json
 from .pubsub_manager import PubSubManager
 
 
@@ -23,7 +22,17 @@ class ZmqManager(PubSubManager):  # pragma: no cover
                     notifications. Must be the same in all the servers.
     :param write_only: If set to ``True``, only initialize to emit events. The
                        default of ``False`` initializes the class for emitting
-                       and receiving.
+                       and receiving. A write-only instance can be used
+                       independently of the server to emit to clients from an
+                       external process.
+    :param logger: a custom logger to log it. If not given, the server logger
+                   is used.
+    :param json: An alternative JSON module to use for encoding and decoding
+                 packets. Custom json modules must have ``dumps`` and ``loads``
+                 functions that are compatible with the standard library
+                 versions. This setting is only used when ``write_only`` is set
+                 to ``True``. Otherwise the JSON module configured in the
+                 server is used.
 
     A zmq message broker must be running for the zmq_manager to work.
     you can write your own or adapt one from the following simple broker
@@ -42,10 +51,8 @@ class ZmqManager(PubSubManager):  # pragma: no cover
     """
     name = 'zmq'
 
-    def __init__(self, url='zmq+tcp://localhost:5555+5556',
-                 channel='socketio',
-                 write_only=False,
-                 logger=None):
+    def __init__(self, url='zmq+tcp://localhost:5555+5556', channel='socketio',
+                 write_only=False, logger=None, json=None):
         try:
             from eventlet.green import zmq
         except ImportError:
@@ -57,7 +64,8 @@ def __init__(self, url='zmq+tcp://localhost:5555+5556',
         if not (url.startswith('zmq+tcp://') and r.search(url)):
             raise RuntimeError('unexpected connection string: ' + url)
 
-        super().__init__(channel=channel, write_only=write_only, logger=logger)
+        super().__init__(channel=channel, write_only=write_only, logger=logger,
+                         json=json)
         url = url.replace('zmq+', '')
         (sink_url, sub_port) = url.split('+')
         sink_port = sink_url.split(':')[-1]
@@ -75,7 +83,7 @@ def __init__(self, url='zmq+tcp://localhost:5555+5556',
         self.channel = channel
 
     def _publish(self, data):
-        packed_data = json.dumps(
+        packed_data = self.json.dumps(
             {
                 'type': 'message',
                 'channel': self.channel,
@@ -94,7 +102,7 @@ def _listen(self):
         for message in self.zmq_listen():
             if isinstance(message, bytes):
                 try:
-                    message = json.loads(message)
+                    message = self.json.loads(message)
                 except Exception:
                     pass
             if isinstance(message, dict) and \
diff --git a/tests/async/test_pubsub_manager.py b/tests/async/test_pubsub_manager.py
index abf41a24..40966bf8 100644
--- a/tests/async/test_pubsub_manager.py
+++ b/tests/async/test_pubsub_manager.py
@@ -5,8 +5,10 @@
 
 import pytest
 
+from engineio.packet import Packet as EIOPacket
 from socketio import async_manager
 from socketio import async_pubsub_manager
+from socketio import async_server
 from socketio import packet
 
 
@@ -846,3 +848,14 @@ async def messages():
         self.pm._handle_emit.assert_awaited_with(
             {'method': 'emit', 'value': 'bar', 'host_id': 'x'}
         )
+
+    def test_custom_json(self):
+        saved_json = packet.Packet.json
+
+        cm = async_pubsub_manager.AsyncPubSubManager(json='foo')
+        assert cm.json == 'foo'
+        async_server.AsyncServer(json='bar', client_manager=cm)
+        assert cm.json == 'bar'
+
+        packet.Packet.json = saved_json
+        EIOPacket.json = saved_json
diff --git a/tests/async/test_redis_manager.py b/tests/async/test_redis_manager.py
index 046c26d2..16fa4caf 100644
--- a/tests/async/test_redis_manager.py
+++ b/tests/async/test_redis_manager.py
@@ -2,8 +2,10 @@
 import redis
 import valkey
 
-from socketio import async_redis_manager
+from engineio.packet import Packet as EIOPacket
+from socketio import async_redis_manager, AsyncServer
 from socketio.async_redis_manager import AsyncRedisManager
+from socketio.packet import Packet
 
 
 class TestAsyncRedisManager:
@@ -109,3 +111,14 @@ def test_valkey_connect(self):
             assert isinstance(c.redis, valkey.asyncio.Valkey)
 
         async_redis_manager.aioredis = saved_redis
+
+    def test_custom_json(self):
+        saved_json = Packet.json
+
+        cm = AsyncRedisManager('redis://', json='foo')
+        assert cm.json == 'foo'
+        AsyncServer(json='bar', client_manager=cm)
+        assert cm.json == 'bar'
+
+        Packet.json = saved_json
+        EIOPacket.json = saved_json
diff --git a/tests/common/test_pubsub_manager.py b/tests/common/test_pubsub_manager.py
index 91b77854..252c77f8 100644
--- a/tests/common/test_pubsub_manager.py
+++ b/tests/common/test_pubsub_manager.py
@@ -5,9 +5,11 @@
 
 import pytest
 
+from engineio.packet import Packet as EIOPacket
 from socketio import manager
 from socketio import pubsub_manager
 from socketio import packet
+from socketio import server
 
 
 class TestPubSubManager:
@@ -822,3 +824,14 @@ def messages():
         self.pm._handle_emit.assert_called_with(
             {'method': 'emit', 'value': 'bar', 'host_id': 'x'}
         )
+
+    def test_custom_json(self):
+        saved_json = packet.Packet.json
+
+        cm = pubsub_manager.PubSubManager(json='foo')
+        assert cm.json == 'foo'
+        server.Server(json='bar', client_manager=cm)
+        assert cm.json == 'bar'
+
+        packet.Packet.json = saved_json
+        EIOPacket.json = saved_json
diff --git a/tests/common/test_redis_manager.py b/tests/common/test_redis_manager.py
index dbc927e4..3f4e29c6 100644
--- a/tests/common/test_redis_manager.py
+++ b/tests/common/test_redis_manager.py
@@ -2,7 +2,9 @@
 import redis
 import valkey
 
-from socketio import redis_manager
+from engineio.packet import Packet as EIOPacket
+from socketio import redis_manager, Server
+from socketio.packet import Packet
 from socketio.redis_manager import RedisManager, parse_redis_sentinel_url
 
 
@@ -144,3 +146,14 @@ def test_sentinel_url_parser(self, rtype):
             'myredis',
             {'username': 'user', 'password': 'password', 'db': 0}
         )
+
+    def test_custom_json(self):
+        saved_json = Packet.json
+
+        cm = RedisManager('redis://', json='foo')
+        assert cm.json == 'foo'
+        Server(json='bar', client_manager=cm)
+        assert cm.json == 'bar'
+
+        Packet.json = saved_json
+        EIOPacket.json = saved_json
diff --git a/tox.ini b/tox.ini
index 02297a2c..0ffa92e7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,7 +14,7 @@ python =
 [testenv]
 commands=
     pip install -e .
-    pytest -p no:logging --timeout=60 --cov=socketio --cov-branch --cov-report=term-missing --cov-report=xml
+    pytest -p no:logging --timeout=60 --cov=socketio --cov-branch --cov-report=term-missing --cov-report=xml {posargs}
 deps=
     simple-websocket
     uvicorn