diff --git a/tests/test_client.py b/tests/test_client.py
index 4f513ac..a2ce5a8 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -176,6 +176,7 @@ def test_get_object(httpserver):
 
 def test_patch_object(httpserver):
   obj = Object("dummy_type", "dummy_id", {"foo": 1, "bar": 2})
+  obj._context_attributes = {"a": "b"}  # pylint: disable=protected-access
   obj.foo = 2
 
   httpserver.expect_request(
@@ -191,6 +192,7 @@ def test_patch_object(httpserver):
               "attributes": {
                   "foo": 2,
               },
+              "context_attributes": {"a": "b"}
           }
       }
   )
diff --git a/vt/client.py b/vt/client.py
index fee750e..4fc7c5f 100644
--- a/vt/client.py
+++ b/vt/client.py
@@ -15,6 +15,7 @@
 
 import asyncio
 import base64
+import functools
 import io
 import json
 import typing
@@ -25,6 +26,7 @@
 from .feed import Feed, FeedType
 from .iterator import Iterator
 from .object import Object
+from .object import UserDictJsonEncoder
 from .utils import make_sync
 from .version import __version__
 
@@ -267,6 +269,7 @@ def _get_session(self) -> aiohttp.ClientSession:
           headers=headers,
           trust_env=self._trust_env,
           timeout=aiohttp.ClientTimeout(total=self._timeout),
+          json_serialize=functools.partial(json.dumps, cls=UserDictJsonEncoder)
       )
     return self._session
 
diff --git a/vt/object.py b/vt/object.py
index fd3a668..58153e1 100644
--- a/vt/object.py
+++ b/vt/object.py
@@ -16,6 +16,7 @@
 import collections
 import datetime
 import functools
+import json
 import re
 import typing
 
@@ -51,6 +52,15 @@ def __delitem__(self, item):
     super().__delitem__(item)
 
 
+class UserDictJsonEncoder(json.JSONEncoder):
+  """Custom json encoder for UserDict objects."""
+
+  def default(self, o):
+    if isinstance(o, collections.UserDict):
+      return o.data
+    return super().default(o)
+
+
 class Object:
   """This class encapsulates any type of object in the VirusTotal API.