diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index ca608a9..0559961 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,6 +1,7 @@
 Version Next
 
- * ...
+ * Port test runner to pytest.
+ * Fix compatibility issue with Werkezeug 3 related to deprecated ``request.charset``.
 
 Version 0.39
 
diff --git a/Makefile b/Makefile
index 991e524..b3f5b84 100644
--- a/Makefile
+++ b/Makefile
@@ -31,7 +31,7 @@ lint: env/.done
 
 .PHONY: test
 test: env/.done
-	env/bin/python setup.py test
+	env/bin/pytest
 
 .PHONY: tox
 tox: env/bin/tox
diff --git a/README.rst b/README.rst
index fd793ac..f5ea5ce 100644
--- a/README.rst
+++ b/README.rst
@@ -152,7 +152,7 @@ Development
 
 To run a single test module invoke::
 
-    python setup.py test --test-suite acceptable.tests.test_module
+    env/bin/pytest acceptable/tests/test_module.py
 
 or::
 
diff --git a/acceptable/_validation.py b/acceptable/_validation.py
index 5efa375..51f9028 100644
--- a/acceptable/_validation.py
+++ b/acceptable/_validation.py
@@ -138,7 +138,8 @@ def wrapper(*args, **kwargs):
         # is not informative enough.
         if payload is None:
             try:
-                payload = json.loads(request.data.decode(request.charset))
+                charset = request.mimetype_params.get("charset", "utf-8")
+                payload = json.loads(request.data.decode(charset))
             except ValueError as e:
                 raise DataValidationError(
                     ["Error decoding JSON request body: %s" % str(e)]
diff --git a/acceptable/openapi.py b/acceptable/openapi.py
index 866528a..3296da3 100644
--- a/acceptable/openapi.py
+++ b/acceptable/openapi.py
@@ -99,7 +99,7 @@ def _to_dict(source: Any):
         return source._to_dict()  # noqa
     elif isinstance(source, dict):
         return {key: _to_dict(value) for key, value in source.items()}
-    elif type(source) == list:
+    elif type(source) is list:
         return [_to_dict(value) for value in source]
     elif hasattr(source, "__dict__"):
         return {key: _to_dict(value) for key, value in source.__dict__.items()}
diff --git a/acceptable/tests/test_service.py b/acceptable/tests/test_service.py
index 244369e..85ccd24 100644
--- a/acceptable/tests/test_service.py
+++ b/acceptable/tests/test_service.py
@@ -434,7 +434,8 @@ def match(self, response):
             return mismatch
         data = response.data
         if self._decode:
-            data = data.decode(response.charset)
+            charset = response.mimetype_params.get("charset", "utf-8")
+            data = data.decode(charset)
         return self.expected_content.match(data)
 
     def __str__(self):
diff --git a/acceptable/tests/test_validation.py b/acceptable/tests/test_validation.py
index 6e9f7d6..4f756cd 100644
--- a/acceptable/tests/test_validation.py
+++ b/acceptable/tests/test_validation.py
@@ -153,7 +153,8 @@ def view():
         self.assertRaises(AssertionError, app.post_json, [])
 
     def assertResponseJsonEqual(self, response, expected_json):
-        data = json.loads(response.data.decode(response.charset))
+        charset = response.mimetype_params.get("charset", "utf-8")
+        data = json.loads(response.data.decode(charset))
         self.assertEqual(expected_json, data)
 
     def test_passes_on_good_payload_single_return_parameter(self):
diff --git a/pyproject.toml b/pyproject.toml
index b58143b..623ea06 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,3 +5,9 @@ skip-magic-trailing-comma = true
 [tool.isort]
 profile = "black"
 skip = ["env", ".tox"]
+
+[tool.pytest.ini_options]
+addopts = "--cov=acceptable"
+
+[tool.coverage.report]
+omit = ["acceptable/tests/*"]
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 38ba335..6cede52 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -3,6 +3,8 @@ coveralls
 flake8
 fixtures
 isort
+pytest
+pytest-cov
 testscenarios
 testtools
 responses
diff --git a/tox.ini b/tox.ini
index 0d76291..79c0e6f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -15,7 +15,7 @@ extras =
     flask
     django
 commands =
-    coverage run --source acceptable --omit "acceptable/tests/*" setup.py test {posargs}
+    pytest {posargs}
 passenv =
     TRAVIS
     TRAVIS_BRANCH