diff --git a/changelog.d/8259.misc b/changelog.d/8259.misc
new file mode 100644
index 0000000000000000000000000000000000000000..a26779a664c773ad144cf801edad54ef9f925b2e
--- /dev/null
+++ b/changelog.d/8259.misc
@@ -0,0 +1 @@
+Switch to the JSON implementation from the standard library.
diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index 2a2c9e6f131a4f3457853e2665b612bb8a073e41..bb33345be60e0d48b80209baa7440bd0aa378ebc 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -15,10 +15,10 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import json
 from typing import List
 
 import jsonschema
-from canonicaljson import json
 from jsonschema import FormatChecker
 
 from synapse.api.constants import EventContentFields
diff --git a/synapse/app/admin_cmd.py b/synapse/app/admin_cmd.py
index b6c90856706cfab21031cc20c476c71b161ecde8..7d309b1bb00a292aef52b9bf11aa325add9093a2 100644
--- a/synapse/app/admin_cmd.py
+++ b/synapse/app/admin_cmd.py
@@ -14,13 +14,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import argparse
+import json
 import logging
 import os
 import sys
 import tempfile
 
-from canonicaljson import json
-
 from twisted.internet import defer, task
 
 import synapse
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 3ad4b28fc73b61c32e853f79dd4dfe9443b6531b..b2355700adbcfdfaf3f3967555738ca390a0ffe1 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -13,11 +13,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import json
 import logging
 import re
 
 import attr
-from canonicaljson import json
 
 from twisted.internet import defer, task
 
diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
index 0e445e01d7737e022bf258e81018e46b5cca3009..bf094c9386784f51c8d13ae94dfaa735bf9a2a17 100644
--- a/synapse/util/frozenutils.py
+++ b/synapse/util/frozenutils.py
@@ -13,7 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from canonicaljson import json
+import json
+
 from frozendict import frozendict
 
 
@@ -66,5 +67,5 @@ def _handle_frozendict(obj):
 # A JSONEncoder which is capable of encoding frozendicts without barfing.
 # Additionally reduce the whitespace produced by JSON encoding.
 frozendict_json_encoder = json.JSONEncoder(
-    default=_handle_frozendict, separators=(",", ":"),
+    allow_nan=False, separators=(",", ":"), default=_handle_frozendict,
 )