diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index e5bd811..efeb672 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -23,7 +23,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: "3.7"
+          python-version: "3.8"
       - run: pip install tox
       - run: tox -e ${{ matrix.toxenv }}
 
@@ -31,7 +31,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "pypy-3.7"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "pypy-3.7"]
 
     steps:
       - uses: actions/checkout@v2
@@ -39,7 +39,7 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
       - run: pip install tox
-      - run: tox -e py
+      - run: tox
 
   packaging:
     runs-on: ${{ matrix.os }}
@@ -57,7 +57,7 @@ jobs:
     runs-on: macos-latest
     strategy:
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
       - uses: actions/checkout@v2
@@ -65,5 +65,4 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
       - run: pip install tox
-      - run: tox -e py
-
+      - run: tox
diff --git a/pyproject.toml b/pyproject.toml
index d8c65f4..edee9e3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,8 @@
 [tool.mypy]
 show_error_codes = true
 strict = true
+# specifically this is because there is no typing stubs for immutabledict
+ignore_missing_imports = true
 
 files = ["."]
 
diff --git a/setup.cfg b/setup.cfg
index dd55872..685a63a 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -28,6 +28,10 @@ packages =
 [options.package_data]
 canonicaljson = py.typed
 
+[options.extras_require]
+orjson =
+  orjson; python_version>"3.8"
+
 [flake8]
 # see https://pycodestyle.readthedocs.io/en/latest/intro.html#error-codes
 # for error codes. The ones we ignore are:
diff --git a/src/canonicaljson/__init__.py b/src/canonicaljson/__init__.py
index 3873974..cab7b20 100644
--- a/src/canonicaljson/__init__.py
+++ b/src/canonicaljson/__init__.py
@@ -15,8 +15,19 @@
 # limitations under the License.
 import functools
 import json
+import math
 from typing import Callable, Generator, Type, TypeVar
 
+use_orjson = False
+try:
+    import orjson
+
+    use_orjson = True
+
+except ImportError:
+    orjson = None  # type: ignore [assignment]
+
+
 __version__ = "2.0.0"
 
 
@@ -74,12 +85,34 @@ def register_preserialisation_callback(
 )
 
 
+def check_for_nan_and_inf(data: object) -> None:
+    """
+    Recursively checks for NaN and Inf values in a dictionary or list.
+    Raises ValueError if found.
+    """
+    if isinstance(data, dict):
+        for key, value in data.items():
+            check_for_nan_and_inf(value)
+    elif isinstance(data, list):
+        for item in data:
+            check_for_nan_and_inf(item)
+    elif isinstance(data, float):
+        if math.isnan(data) or math.isinf(data):
+            raise ValueError
+
+
 def encode_canonical_json(data: object) -> bytes:
     """Encodes the given `data` as a UTF-8 canonical JSON bytestring.
 
     This encoding is the shortest possible. Dictionary keys are
     lexicographically sorted by unicode code point.
     """
+    if use_orjson:
+        check_for_nan_and_inf(data)
+        return orjson.dumps(
+            data, default=_preprocess_for_serialisation, option=orjson.OPT_SORT_KEYS
+        )
+
     s = _canonical_encoder.encode(data)
     return s.encode("utf-8")
 
@@ -101,6 +134,13 @@ def iterencode_canonical_json(data: object) -> Generator[bytes, None, None]:
 def encode_pretty_printed_json(data: object) -> bytes:
     """Encodes the given `data` as a UTF-8 human-readable JSON bytestring."""
 
+    if use_orjson:
+        # Unfortunately, orjson decided to hardcode their indent to 2
+        check_for_nan_and_inf(data)
+        return orjson.dumps(
+            data, default=_preprocess_for_serialisation, option=orjson.OPT_INDENT_2
+        )
+
     return _pretty_encoder.encode(data).encode("utf-8")
 
 
diff --git a/tests/test_canonicaljson.py b/tests/test_canonicaljson.py
index 2ae6f7f..9481533 100644
--- a/tests/test_canonicaljson.py
+++ b/tests/test_canonicaljson.py
@@ -15,8 +15,11 @@
 # limitations under the License.
 import unittest
 from math import inf, nan
+from typing import Any, Union
 from unittest.mock import Mock
 
+from immutabledict import immutabledict
+
 from canonicaljson import (
     encode_canonical_json,
     encode_pretty_printed_json,
@@ -25,6 +28,12 @@
     register_preserialisation_callback,
 )
 
+try:
+    import orjson
+
+except ImportError:
+    orjson = None  # type: ignore [assignment]
+
 
 class TestCanonicalJson(unittest.TestCase):
     def test_encode_canonical(self) -> None:
@@ -98,10 +107,16 @@ def test_encode_pretty_printed(self) -> None:
         self.assertEqual(encode_pretty_printed_json({}), b"{}")
         self.assertEqual(list(iterencode_pretty_printed_json({})), [b"{}"])
 
+        if orjson is not None:
+            # orjson's pretty print style is a flag option and is hardcoded to "2",
+            # so this will be slightly different.
+            comparison = b'{\n  "la merde amus\xc3\xa9e": "\xF0\x9F\x92\xA9"\n}'
+        else:
+            comparison = b'{\n    "la merde amus\xc3\xa9e": "\xF0\x9F\x92\xA9"\n}'
         # non-ascii should come out utf8-encoded.
         self.assertEqual(
             encode_pretty_printed_json({"la merde amusée": "💩"}),
-            b'{\n    "la merde amus\xc3\xa9e": "\xF0\x9F\x92\xA9"\n}',
+            comparison,
         )
 
     def test_unknown_type(self) -> None:
@@ -136,6 +151,68 @@ def test_invalid_float_values(self) -> None:
         with self.assertRaises(ValueError):
             encode_pretty_printed_json(nan)
 
+    def test_invalid_nested_float_values(self) -> None:
+        """Infinity/-Infinity/NaN are not allowed in canonicaljson."""
+        data_with_inf = {"a": 1, "b": float("inf")}
+        data_with_neg_inf = {"a": 1, "b": -float("inf")}
+        data_with_nan = {"a": 1, "b": float("nan")}
+        list_with_inf = {"a": [1, float("inf")]}
+        list_with_neg_inf = {"a": [1, -float("inf")]}
+        list_with_nan = {"a": [1, float("nan")]}
+
+        with self.assertRaises(ValueError):
+            encode_canonical_json(data_with_inf)
+
+        with self.assertRaises(ValueError):
+            encode_pretty_printed_json(data_with_inf)
+
+        with self.assertRaises(ValueError):
+            encode_canonical_json(data_with_neg_inf)
+
+        with self.assertRaises(ValueError):
+            encode_pretty_printed_json(data_with_neg_inf)
+
+        with self.assertRaises(ValueError):
+            encode_canonical_json(data_with_nan)
+
+        with self.assertRaises(ValueError):
+            encode_pretty_printed_json(data_with_nan)
+
+        with self.assertRaises(ValueError):
+            encode_canonical_json(list_with_inf)
+
+        with self.assertRaises(ValueError):
+            encode_pretty_printed_json(list_with_inf)
+
+        with self.assertRaises(ValueError):
+            encode_canonical_json(list_with_neg_inf)
+
+        with self.assertRaises(ValueError):
+            encode_pretty_printed_json(list_with_neg_inf)
+
+        with self.assertRaises(ValueError):
+            encode_canonical_json(list_with_nan)
+
+        with self.assertRaises(ValueError):
+            encode_pretty_printed_json(list_with_nan)
+
+    def test_immutable_dict_handling(self) -> None:
+        im_d: immutabledict[str, Union[str, int]] = immutabledict(
+            {"key1": "value1", "key2": 42}
+        )
+
+        # Lifted from Synapse's __init__.py
+        def _immutabledict_cb(d: immutabledict[str, Any]) -> Any:
+            try:
+                return d._dict
+            except Exception:
+                # Paranoia: fall back to a `dict()` call, in case a future version of
+                # immutabledict removes `_dict` from the implementation.
+                return dict(d)
+
+        register_preserialisation_callback(immutabledict, _immutabledict_cb)
+        encode_canonical_json(im_d)
+
     def test_encode_unknown_class_raises(self) -> None:
         class C:
             pass
diff --git a/tox.ini b/tox.ini
index 32606d7..bc00fef 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,34 +1,57 @@
 [tox]
-envlist = packaging, pep8, black, py37, py38, py39, py310, pypy3, mypy, isort
+envlist = packaging, pep8, black, py{38,39,310,311,312,313}-base, py{38,39,310,311,312,313}-orjson, pypy3, mypy, isort, coverage
 isolated_build = True
 
 [testenv:py]
 deps =
     coverage
+    immutabledict
+
+[testenv:coverage]
+; Use this after the other coverage steps have run, to combine and summarize the results
+skip_install = True
+deps =
+    {[testenv:py]deps}
 
 commands =
-    coverage run --source canonicaljson -m unittest
+    coverage combine
     coverage report -m --fail-under 100
 
+[testenv:py{37,38,39,310,311,312,313}-base]
+deps =
+    {[testenv:py]deps}
+commands =
+    coverage run -p --source canonicaljson -m unittest
+
+[testenv:py{37,38,39,310,311,312,313}-orjson]
+deps =
+    {[testenv:py]deps}
+
+extras =
+    orjson
+
+commands =
+    coverage run -p --source canonicaljson -m unittest
+
 [testenv:packaging]
 deps =
     check-manifest
 commands = check-manifest
 
 [testenv:pep8]
-basepython = python3.7
+basepython = python3.8
 deps =
     flake8
 commands = flake8 src tests
 
 [testenv:isort]
-basepython = python3.7
+basepython = python3.8
 deps =
     isort
 commands = isort --check src tests
 
 [testenv:black]
-basepython = python3.7
+basepython = python3.8
 deps =
     black==23.1.0
 commands = python -m black --check --diff src tests
@@ -37,4 +60,5 @@ commands = python -m black --check --diff src tests
 deps =
     mypy==1.0
     types-setuptools==57.4.14
+    types-orjson==3.6.0
 commands = mypy src tests