diff --git a/changelog.d/7800.misc b/changelog.d/7800.misc
new file mode 100644
index 0000000000..ce2346b3d4
--- /dev/null
+++ b/changelog.d/7800.misc
@@ -0,0 +1 @@
+Switch from simplejson to the standard library json.
diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index ea5937a20c..0f453ff0a8 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -18,18 +18,11 @@ The VALID_SERVER_COMMANDS and VALID_CLIENT_COMMANDS define which commands are
 allowed to be sent by which side.
 """
 import abc
+import json
 import logging
-import platform
 from typing import Tuple, Type
 
-if platform.python_implementation() == "PyPy":
-    import json
-
-    _json_encoder = json.JSONEncoder()
-else:
-    import simplejson as json  # type: ignore[no-redef]  # noqa: F821
-
-    _json_encoder = json.JSONEncoder(namedtuple_as_object=False)  # type: ignore[call-arg]  # noqa: F821
+_json_encoder = json.JSONEncoder()
 
 logger = logging.getLogger(__name__)
 
diff --git a/synapse/storage/data_stores/main/schema/delta/25/fts.py b/synapse/storage/data_stores/main/schema/delta/25/fts.py
index 4b2ffd35fd..ee675e71ff 100644
--- a/synapse/storage/data_stores/main/schema/delta/25/fts.py
+++ b/synapse/storage/data_stores/main/schema/delta/25/fts.py
@@ -11,11 +11,9 @@
 # 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
 import logging
 
-import simplejson
-
 from synapse.storage.engines import PostgresEngine, Sqlite3Engine
 from synapse.storage.prepare_database import get_statements
 
@@ -66,7 +64,7 @@ def run_create(cur, database_engine, *args, **kwargs):
             "max_stream_id_exclusive": max_stream_id + 1,
             "rows_inserted": 0,
         }
-        progress_json = simplejson.dumps(progress)
+        progress_json = json.dumps(progress)
 
         sql = (
             "INSERT into background_updates (update_name, progress_json)"
diff --git a/synapse/storage/data_stores/main/schema/delta/27/ts.py b/synapse/storage/data_stores/main/schema/delta/27/ts.py
index 414f9f5aa0..b7972cfa8e 100644
--- a/synapse/storage/data_stores/main/schema/delta/27/ts.py
+++ b/synapse/storage/data_stores/main/schema/delta/27/ts.py
@@ -11,11 +11,9 @@
 # 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
 import logging
 
-import simplejson
-
 from synapse.storage.prepare_database import get_statements
 
 logger = logging.getLogger(__name__)
@@ -45,7 +43,7 @@ def run_create(cur, database_engine, *args, **kwargs):
             "max_stream_id_exclusive": max_stream_id + 1,
             "rows_inserted": 0,
         }
-        progress_json = simplejson.dumps(progress)
+        progress_json = json.dumps(progress)
 
         sql = (
             "INSERT into background_updates (update_name, progress_json)"
diff --git a/synapse/storage/data_stores/main/schema/delta/31/search_update.py b/synapse/storage/data_stores/main/schema/delta/31/search_update.py
index 7d8ca5f93f..63b757ade6 100644
--- a/synapse/storage/data_stores/main/schema/delta/31/search_update.py
+++ b/synapse/storage/data_stores/main/schema/delta/31/search_update.py
@@ -11,11 +11,9 @@
 # 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
 import logging
 
-import simplejson
-
 from synapse.storage.engines import PostgresEngine
 from synapse.storage.prepare_database import get_statements
 
@@ -50,7 +48,7 @@ def run_create(cur, database_engine, *args, **kwargs):
             "rows_inserted": 0,
             "have_added_indexes": False,
         }
-        progress_json = simplejson.dumps(progress)
+        progress_json = json.dumps(progress)
 
         sql = (
             "INSERT into background_updates (update_name, progress_json)"
diff --git a/synapse/storage/data_stores/main/schema/delta/33/event_fields.py b/synapse/storage/data_stores/main/schema/delta/33/event_fields.py
index bff1256a7b..a3e81eeac7 100644
--- a/synapse/storage/data_stores/main/schema/delta/33/event_fields.py
+++ b/synapse/storage/data_stores/main/schema/delta/33/event_fields.py
@@ -11,11 +11,9 @@
 # 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
 import logging
 
-import simplejson
-
 from synapse.storage.prepare_database import get_statements
 
 logger = logging.getLogger(__name__)
@@ -45,7 +43,7 @@ def run_create(cur, database_engine, *args, **kwargs):
             "max_stream_id_exclusive": max_stream_id + 1,
             "rows_inserted": 0,
         }
-        progress_json = simplejson.dumps(progress)
+        progress_json = json.dumps(progress)
 
         sql = (
             "INSERT into background_updates (update_name, progress_json)"