diff --git a/firetail/apps/flask_app.py b/firetail/apps/flask_app.py
index 9294887..e0a7072 100644
--- a/firetail/apps/flask_app.py
+++ b/firetail/apps/flask_app.py
@@ -2,18 +2,17 @@
 This module defines a FlaskApp, a Firetail application to wrap a Flask application.
 """
 
-import datetime
 import logging
 import pathlib
-from decimal import Decimal
 from types import FunctionType  # NOQA
 
 import flask
 import werkzeug.exceptions
-from flask import json, signals
+from flask import signals
 
 from ..apis.flask_api import FlaskApi
 from ..exceptions import ProblemException
+from ..jsonifier import wrap_default
 from ..problem import problem
 from .abstract import AbstractApp
 
@@ -33,7 +32,7 @@ def __init__(self, import_name, server="flask", extra_files=None, **kwargs):
 
     def create_app(self):
         app = flask.Flask(self.import_name, **self.server_args)
-        app.json_encoder = FlaskJSONEncoder
+        app.json = FlaskJSONProvider(app)
         app.url_map.converters["float"] = NumberConverter
         app.url_map.converters["int"] = IntegerConverter
         return app
@@ -148,24 +147,12 @@ def run(self, port=None, server=None, debug=None, host=None, extra_files=None, *
             raise Exception(f"Server {self.server} not recognized")
 
 
-class FlaskJSONEncoder(json.JSONEncoder):
+class FlaskJSONProvider(flask.json.provider.DefaultJSONProvider):
+    """Custom JSONProvider which adds firetail defaults on top of Flask's"""
+
+    @wrap_default
     def default(self, o):
-        if isinstance(o, datetime.datetime):
-            if o.tzinfo:
-                # eg: '2015-09-25T23:14:42.588601+00:00'
-                return o.isoformat("T")
-            else:
-                # No timezone present - assume UTC.
-                # eg: '2015-09-25T23:14:42.588601Z'
-                return o.isoformat("T") + "Z"
-
-        if isinstance(o, datetime.date):
-            return o.isoformat()
-
-        if isinstance(o, Decimal):
-            return float(o)
-
-        return json.JSONEncoder.default(self, o)
+        return super().default(o)
 
 
 class NumberConverter(werkzeug.routing.BaseConverter):
diff --git a/firetail/jsonifier.py b/firetail/jsonifier.py
index ceffbe5..c8d681d 100644
--- a/firetail/jsonifier.py
+++ b/firetail/jsonifier.py
@@ -3,21 +3,26 @@
 """
 
 import datetime
+import functools
 import json
+import typing as t
 import uuid
+from decimal import Decimal
 
 
-class JSONEncoder(json.JSONEncoder):
-    """The default Firetail JSON encoder. Handles extra types compared to the
-    built-in :class:`json.JSONEncoder`. # noqa RST304
+def wrap_default(default_fn: t.Callable) -> t.Callable:
+    """The Firetail defaults for JSON encoding. Handles extra types compared to the
+    built-in :class:`json.JSONEncoder`.
 
-    -   :class:`datetime.datetime` and :class:`datetime.date` are   # noqa RST304
+    -   :class:`datetime.datetime` and :class:`datetime.date` are
         serialized to :rfc:`822` strings. This is the same as the HTTP
         date format.
-    -   :class:`uuid.UUID` is serialized to a string.  # noqa RST304
+    -   :class:`decimal.Decimal` is serialized to a float.
+    -   :class:`uuid.UUID` is serialized to a string.
     """
 
-    def default(self, o):
+    @functools.wraps(default_fn)
+    def wrapped_default(self, o):
         if isinstance(o, datetime.datetime):
             if o.tzinfo:
                 # eg: '2015-09-25T23:14:42.588601+00:00'
@@ -30,10 +35,25 @@ def default(self, o):
         if isinstance(o, datetime.date):
             return o.isoformat()
 
+        if isinstance(o, Decimal):
+            return float(o)
+
         if isinstance(o, uuid.UUID):
             return str(o)
 
-        return json.JSONEncoder.default(self, o)
+        return default_fn(o)
+
+    return wrapped_default
+
+
+class JSONEncoder(json.JSONEncoder):
+    """The default Firetail JSON encoder. Handles extra types compared to the
+    built-in :class:`json.JSONEncoder`.
+    """
+
+    @wrap_default
+    def default(self, o):
+        return super().default(o)
 
 
 class Jsonifier:
@@ -48,6 +68,7 @@ def __init__(self, json_=json, **kwargs):
         """
         self.json = json_
         self.dumps_args = kwargs
+        self.dumps_args.setdefault("cls", JSONEncoder)
 
     def dumps(self, data, **kwargs):
         """Central point where JSON serialization happens inside
diff --git a/firetail/middleware/swagger_ui.py b/firetail/middleware/swagger_ui.py
index 88e78a6..3b619c4 100644
--- a/firetail/middleware/swagger_ui.py
+++ b/firetail/middleware/swagger_ui.py
@@ -12,7 +12,6 @@
 from starlette.types import ASGIApp, Receive, Scope, Send
 
 from firetail.apis import AbstractSwaggerUIAPI
-from firetail.jsonifier import JSONEncoder, Jsonifier
 from firetail.utils import yamldumper
 
 from .base import AppMiddleware
@@ -198,7 +197,3 @@ async def _get_swagger_ui_config(self, request):
             media_type="application/json",
             content=self.jsonifier.dumps(self.options.openapi_console_ui_config),
         )
-
-    @classmethod
-    def _set_jsonifier(cls):
-        cls.jsonifier = Jsonifier(cls=JSONEncoder)
diff --git a/requirements.txt b/requirements.txt
index 5981713..19c2e2b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,13 +1,13 @@
 a2wsgi==1.4
 clickclick==1.2
-flask[async]==2.2.5
+flask[async]==2.3.3
 inflection==0.3.1
 jsonschema==4.0.1
 PyJWT==2.4.0
 PyYAML==6.0.1
 requests==2.31.0
 starlette==0.27.0
-werkzeug==2.2.3
+werkzeug==3.0.1
 aiohttp_jinja2
 aiohttp
 aiohttp_remotes
diff --git a/setup.py b/setup.py
index 21538c9..c66cf9d 100644
--- a/setup.py
+++ b/setup.py
@@ -26,14 +26,14 @@ def read_version(package):
     "PyJWT>=2.4.0",
     "requests>=2.31,<3",
     "inflection>=0.3.1,<0.6",
-    "werkzeug>=2.2.2,<3",
+    "werkzeug>=3.0.1",
     "starlette>=0.27,<1",
 ]
 
 swagger_ui_require = "swagger-ui-bundle>=0.0.2,<0.1"
 
 flask_require = [
-    "flask[async]>=2.2.5,<3.0",
+    "flask[async]>=2.3.0,<3.0",
     "a2wsgi>=1.4,<2",
 ]
 
diff --git a/tests/api/test_parameters.py b/tests/api/test_parameters.py
index 87f992b..027e2c0 100644
--- a/tests/api/test_parameters.py
+++ b/tests/api/test_parameters.py
@@ -516,7 +516,7 @@ def test_get_unicode_request(simple_app):
 
 def test_cookie_param(simple_app):
     app_client = simple_app.app.test_client()
-    app_client.set_cookie("localhost", "test_cookie", "hello")
+    app_client.set_cookie("test_cookie", "hello")
     response = app_client.get("/v1.0/test-cookie-param")
     assert response.status_code == 200
     assert response.json == {"cookie_value": "hello"}
diff --git a/tests/api/test_responses.py b/tests/api/test_responses.py
index 4422ada..3151609 100644
--- a/tests/api/test_responses.py
+++ b/tests/api/test_responses.py
@@ -2,9 +2,10 @@
 from struct import unpack
 
 import yaml
-from firetail.apps.flask_app import FlaskJSONEncoder
 from werkzeug.test import Client, EnvironBuilder
 
+from firetail.apps.flask_app import FlaskJSONProvider
+
 
 def test_app(simple_app):
     assert simple_app.port == 5001
@@ -242,11 +243,11 @@ def test_nested_additional_properties(simple_openapi_app):
 
 
 def test_custom_encoder(simple_app):
-    class CustomEncoder(FlaskJSONEncoder):
+    class CustomEncoder(FlaskJSONProvider):
         def default(self, o):
             if o.__class__.__name__ == "DummyClass":
                 return "cool result"
-            return FlaskJSONEncoder.default(self, o)
+            return FlaskJSONProvider.default(self, o)
 
     flask_app = simple_app.app
     flask_app.json_encoder = CustomEncoder
diff --git a/tests/test_flask_encoder.py b/tests/test_flask_encoder.py
index d9e9060..730ec6f 100644
--- a/tests/test_flask_encoder.py
+++ b/tests/test_flask_encoder.py
@@ -5,25 +5,26 @@
 
 import pytest
 from conftest import build_app_from_fixture
-from firetail.apps.flask_app import FlaskJSONEncoder
+
+from firetail.apps.flask_app import FlaskJSONProvider
 
 SPECS = ["swagger.yaml", "openapi.yaml"]
 
 
 def test_json_encoder():
-    s = json.dumps({1: 2}, cls=FlaskJSONEncoder)
+    s = json.dumps({1: 2}, cls=FlaskJSONProvider)
     assert '{"1": 2}' == s
 
-    s = json.dumps(datetime.date.today(), cls=FlaskJSONEncoder)
+    s = json.dumps(datetime.date.today(), cls=FlaskJSONProvider)
     assert len(s) == 12
 
-    s = json.dumps(datetime.datetime.utcnow(), cls=FlaskJSONEncoder)
+    s = json.dumps(datetime.datetime.utcnow(), cls=FlaskJSONProvider)
     assert s.endswith('Z"')
 
-    s = json.dumps(Decimal(1.01), cls=FlaskJSONEncoder)
+    s = json.dumps(Decimal(1.01), cls=FlaskJSONProvider)
     assert s == "1.01"
 
-    s = json.dumps(math.expm1(1e-10), cls=FlaskJSONEncoder)
+    s = json.dumps(math.expm1(1e-10), cls=FlaskJSONProvider)
     assert s == "1.00000000005e-10"
 
 
@@ -35,7 +36,7 @@ def utcoffset(self, dt):
         def dst(self, dt):
             return datetime.timedelta(0)
 
-    s = json.dumps(datetime.datetime.now(DummyTimezone()), cls=FlaskJSONEncoder)
+    s = json.dumps(datetime.datetime.now(DummyTimezone()), cls=FlaskJSONProvider)
     assert s.endswith('+00:00"')