diff --git a/CHANGES.md b/CHANGES.md
index 6044fc2a90f3..81f9a1aa2625 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -29,9 +29,9 @@ Bugfixes
 - Return a proper error code when the rooms of an invalid group are requested. ([\#8129](https://github.com/matrix-org/synapse/issues/8129))
 - Fix a bug which could cause a leaked postgres connection if synapse was set to daemonize. ([\#8131](https://github.com/matrix-org/synapse/issues/8131))
 - Clarify the error code if a user tries to register with a numeric ID. This bug was introduced in v1.15.0. ([\#8135](https://github.com/matrix-org/synapse/issues/8135))
-- Fixes a bug where appservices with ratelimiting disabled would still be ratelimited when joining rooms. This bug was introduced in v1.19.0. ([\#8139](https://github.com/matrix-org/synapse/issues/8139))
+- Fix a bug where appservices with ratelimiting disabled would still be ratelimited when joining rooms. This bug was introduced in v1.19.0. ([\#8139](https://github.com/matrix-org/synapse/issues/8139))
 - Fix logging in via OpenID Connect with a provider that uses integer user IDs. ([\#8190](https://github.com/matrix-org/synapse/issues/8190))
-- Fixes a longstanding bug where user directory updates could break when unexpected profile data was included in events. ([\#8223](https://github.com/matrix-org/synapse/issues/8223))
+- Fix a longstanding bug where user directory updates could break when unexpected profile data was included in events. ([\#8223](https://github.com/matrix-org/synapse/issues/8223))
 - Fix a longstanding bug where stats updates could break when unexpected profile data was included in events. ([\#8226](https://github.com/matrix-org/synapse/issues/8226))
 - Fix slow start times for large servers by removing a table scan of the `users` table from startup code. ([\#8271](https://github.com/matrix-org/synapse/issues/8271))
 
@@ -80,7 +80,7 @@ Internal Changes
 - Remove obsolete `order` field from federation send queues. ([\#8245](https://github.com/matrix-org/synapse/issues/8245))
 - Stop sub-classing from object. ([\#8249](https://github.com/matrix-org/synapse/issues/8249))
 - Add more logging to debug slow startup. ([\#8264](https://github.com/matrix-org/synapse/issues/8264))
-- Do not attempt to upgrade upgrade database schema on worker processes. ([\#8266](https://github.com/matrix-org/synapse/issues/8266), [\#8276](https://github.com/matrix-org/synapse/issues/8276))
+- Do not attempt to upgrade database schema on worker processes. ([\#8266](https://github.com/matrix-org/synapse/issues/8266), [\#8276](https://github.com/matrix-org/synapse/issues/8276))
 
 
 Synapse 1.19.1 (2020-08-27)
diff --git a/changelog.d/8243.misc b/changelog.d/8243.misc
new file mode 100644
index 000000000000..f7375d32d33e
--- /dev/null
+++ b/changelog.d/8243.misc
@@ -0,0 +1 @@
+Remove the 'populate_stats_process_rooms_2' background job and restore functionality to 'populate_stats_process_rooms'.
\ No newline at end of file
diff --git a/changelog.d/8259.misc b/changelog.d/8259.misc
new file mode 100644
index 000000000000..a26779a664c7
--- /dev/null
+++ b/changelog.d/8259.misc
@@ -0,0 +1 @@
+Switch to the JSON implementation from the standard library.
diff --git a/changelog.d/8261.misc b/changelog.d/8261.misc
new file mode 100644
index 000000000000..bc91e9375ce0
--- /dev/null
+++ b/changelog.d/8261.misc
@@ -0,0 +1 @@
+Simplify tests that mock asynchronous functions.
diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index 2a2c9e6f131a..bb33345be60e 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 b6c90856706c..7d309b1bb00a 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/storage/databases/main/schema/delta/58/16populate_stats_process_rooms_fix.sql b/synapse/storage/databases/main/schema/delta/58/16populate_stats_process_rooms_fix.sql
new file mode 100644
index 000000000000..55f5d0f7327c
--- /dev/null
+++ b/synapse/storage/databases/main/schema/delta/58/16populate_stats_process_rooms_fix.sql
@@ -0,0 +1,22 @@
+/* Copyright 2020 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * 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.
+ */
+-- This delta file fixes a regression introduced by 58/12room_stats.sql, removing the hacky
+-- populate_stats_process_rooms_2 background job and restores the functionality under the
+-- original name.
+-- See https://github.com/matrix-org/synapse/issues/8238 for details
+
+DELETE FROM background_updates WHERE update_name = 'populate_stats_process_rooms';
+UPDATE background_updates SET update_name = 'populate_stats_process_rooms'
+    WHERE update_name = 'populate_stats_process_rooms_2';
diff --git a/synapse/storage/databases/main/stats.py b/synapse/storage/databases/main/stats.py
index 55a250ef06fd..30840dbbaa31 100644
--- a/synapse/storage/databases/main/stats.py
+++ b/synapse/storage/databases/main/stats.py
@@ -73,9 +73,6 @@ def __init__(self, database: DatabasePool, db_conn, hs):
         self.db_pool.updates.register_background_update_handler(
             "populate_stats_process_rooms", self._populate_stats_process_rooms
         )
-        self.db_pool.updates.register_background_update_handler(
-            "populate_stats_process_rooms_2", self._populate_stats_process_rooms_2
-        )
         self.db_pool.updates.register_background_update_handler(
             "populate_stats_process_users", self._populate_stats_process_users
         )
@@ -148,31 +145,10 @@ def _get_next_batch(txn):
         return len(users_to_work_on)
 
     async def _populate_stats_process_rooms(self, progress, batch_size):
-        """
-        This was a background update which regenerated statistics for rooms.
-
-        It has been replaced by StatsStore._populate_stats_process_rooms_2. This background
-        job has been scheduled to run as part of Synapse v1.0.0, and again now. To ensure
-        someone upgrading from <v1.0.0, this background task has been turned into a no-op
-        so that the potentially expensive task is not run twice.
-
-        Further context: https://github.com/matrix-org/synapse/pull/7977
-        """
-        await self.db_pool.updates._end_background_update(
-            "populate_stats_process_rooms"
-        )
-        return 1
-
-    async def _populate_stats_process_rooms_2(self, progress, batch_size):
-        """
-        This is a background update which regenerates statistics for rooms.
-
-        It replaces StatsStore._populate_stats_process_rooms. See its docstring for the
-        reasoning.
-        """
+        """This is a background update which regenerates statistics for rooms."""
         if not self.stats_enabled:
             await self.db_pool.updates._end_background_update(
-                "populate_stats_process_rooms_2"
+                "populate_stats_process_rooms"
             )
             return 1
 
@@ -189,13 +165,13 @@ def _get_next_batch(txn):
             return [r for r, in txn]
 
         rooms_to_work_on = await self.db_pool.runInteraction(
-            "populate_stats_rooms_2_get_batch", _get_next_batch
+            "populate_stats_rooms_get_batch", _get_next_batch
         )
 
         # No more rooms -- complete the transaction.
         if not rooms_to_work_on:
             await self.db_pool.updates._end_background_update(
-                "populate_stats_process_rooms_2"
+                "populate_stats_process_rooms"
             )
             return 1
 
@@ -204,9 +180,9 @@ def _get_next_batch(txn):
             progress["last_room_id"] = room_id
 
         await self.db_pool.runInteraction(
-            "_populate_stats_process_rooms_2",
+            "_populate_stats_process_rooms",
             self.db_pool.updates._background_update_progress_txn,
-            "populate_stats_process_rooms_2",
+            "populate_stats_process_rooms",
             progress,
         )
 
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 3ad4b28fc73b..b2355700adbc 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 0e445e01d773..bf094c938678 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,
 )
diff --git a/tests/federation/test_complexity.py b/tests/federation/test_complexity.py
index 3d880c499d8b..1471cc1a2872 100644
--- a/tests/federation/test_complexity.py
+++ b/tests/federation/test_complexity.py
@@ -77,11 +77,9 @@ def test_join_too_large(self):
         fed_transport = self.hs.get_federation_transport_client()
 
         # Mock out some things, because we don't want to test the whole join
-        fed_transport.client.get_json = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable({"v1": 9999})
-        )
+        fed_transport.client.get_json = Mock(return_value=make_awaitable({"v1": 9999}))
         handler.federation_handler.do_invite_join = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable(("", 1))
+            return_value=make_awaitable(("", 1))
         )
 
         d = handler._remote_join(
@@ -110,11 +108,9 @@ def test_join_too_large_admin(self):
         fed_transport = self.hs.get_federation_transport_client()
 
         # Mock out some things, because we don't want to test the whole join
-        fed_transport.client.get_json = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable({"v1": 9999})
-        )
+        fed_transport.client.get_json = Mock(return_value=make_awaitable({"v1": 9999}))
         handler.federation_handler.do_invite_join = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable(("", 1))
+            return_value=make_awaitable(("", 1))
         )
 
         d = handler._remote_join(
@@ -150,11 +146,9 @@ def test_join_too_large_once_joined(self):
         fed_transport = self.hs.get_federation_transport_client()
 
         # Mock out some things, because we don't want to test the whole join
-        fed_transport.client.get_json = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable(None)
-        )
+        fed_transport.client.get_json = Mock(return_value=make_awaitable(None))
         handler.federation_handler.do_invite_join = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable(("", 1))
+            return_value=make_awaitable(("", 1))
         )
 
         # Artificially raise the complexity
@@ -208,11 +202,9 @@ def test_join_too_large_no_admin(self):
         fed_transport = self.hs.get_federation_transport_client()
 
         # Mock out some things, because we don't want to test the whole join
-        fed_transport.client.get_json = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable({"v1": 9999})
-        )
+        fed_transport.client.get_json = Mock(return_value=make_awaitable({"v1": 9999}))
         handler.federation_handler.do_invite_join = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable(("", 1))
+            return_value=make_awaitable(("", 1))
         )
 
         d = handler._remote_join(
@@ -240,11 +232,9 @@ def test_join_too_large_admin(self):
         fed_transport = self.hs.get_federation_transport_client()
 
         # Mock out some things, because we don't want to test the whole join
-        fed_transport.client.get_json = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable({"v1": 9999})
-        )
+        fed_transport.client.get_json = Mock(return_value=make_awaitable({"v1": 9999}))
         handler.federation_handler.do_invite_join = Mock(
-            side_effect=lambda *args, **kwargs: make_awaitable(("", 1))
+            return_value=make_awaitable(("", 1))
         )
 
         d = handler._remote_join(
diff --git a/tests/federation/test_federation_sender.py b/tests/federation/test_federation_sender.py
index 5f512ff8bfdf..917762e6b658 100644
--- a/tests/federation/test_federation_sender.py
+++ b/tests/federation/test_federation_sender.py
@@ -34,7 +34,7 @@ class FederationSenderReceiptsTestCases(HomeserverTestCase):
     def make_homeserver(self, reactor, clock):
         mock_state_handler = Mock(spec=["get_current_hosts_in_room"])
         # Ensure a new Awaitable is created for each call.
-        mock_state_handler.get_current_hosts_in_room.side_effect = lambda room_Id: make_awaitable(
+        mock_state_handler.get_current_hosts_in_room.return_value = make_awaitable(
             ["test", "host2"]
         )
         return self.setup_test_homeserver(
diff --git a/tests/handlers/test_auth.py b/tests/handlers/test_auth.py
index c7efd3822d6f..97877c2e42af 100644
--- a/tests/handlers/test_auth.py
+++ b/tests/handlers/test_auth.py
@@ -143,7 +143,7 @@ def test_mau_limits_disabled(self):
     def test_mau_limits_exceeded_large(self):
         self.auth_blocking._limit_usage_by_mau = True
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.large_number_of_users)
+            return_value=make_awaitable(self.large_number_of_users)
         )
 
         with self.assertRaises(ResourceLimitError):
@@ -154,7 +154,7 @@ def test_mau_limits_exceeded_large(self):
             )
 
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.large_number_of_users)
+            return_value=make_awaitable(self.large_number_of_users)
         )
         with self.assertRaises(ResourceLimitError):
             yield defer.ensureDeferred(
@@ -169,7 +169,7 @@ def test_mau_limits_parity(self):
 
         # If not in monthly active cohort
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.auth_blocking._max_mau_value)
+            return_value=make_awaitable(self.auth_blocking._max_mau_value)
         )
         with self.assertRaises(ResourceLimitError):
             yield defer.ensureDeferred(
@@ -179,7 +179,7 @@ def test_mau_limits_parity(self):
             )
 
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.auth_blocking._max_mau_value)
+            return_value=make_awaitable(self.auth_blocking._max_mau_value)
         )
         with self.assertRaises(ResourceLimitError):
             yield defer.ensureDeferred(
@@ -189,10 +189,10 @@ def test_mau_limits_parity(self):
             )
         # If in monthly active cohort
         self.hs.get_datastore().user_last_seen_monthly_active = Mock(
-            side_effect=lambda user_id: make_awaitable(self.hs.get_clock().time_msec())
+            return_value=make_awaitable(self.hs.get_clock().time_msec())
         )
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.auth_blocking._max_mau_value)
+            return_value=make_awaitable(self.auth_blocking._max_mau_value)
         )
         yield defer.ensureDeferred(
             self.auth_handler.get_access_token_for_user_id(
@@ -200,10 +200,10 @@ def test_mau_limits_parity(self):
             )
         )
         self.hs.get_datastore().user_last_seen_monthly_active = Mock(
-            side_effect=lambda user_id: make_awaitable(self.hs.get_clock().time_msec())
+            return_value=make_awaitable(self.hs.get_clock().time_msec())
         )
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.auth_blocking._max_mau_value)
+            return_value=make_awaitable(self.auth_blocking._max_mau_value)
         )
         yield defer.ensureDeferred(
             self.auth_handler.validate_short_term_login_token_and_get_user_id(
@@ -216,7 +216,7 @@ def test_mau_limits_not_exceeded(self):
         self.auth_blocking._limit_usage_by_mau = True
 
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.small_number_of_users)
+            return_value=make_awaitable(self.small_number_of_users)
         )
         # Ensure does not raise exception
         yield defer.ensureDeferred(
@@ -226,7 +226,7 @@ def test_mau_limits_not_exceeded(self):
         )
 
         self.hs.get_datastore().get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.small_number_of_users)
+            return_value=make_awaitable(self.small_number_of_users)
         )
         yield defer.ensureDeferred(
             self.auth_handler.validate_short_term_login_token_and_get_user_id(
diff --git a/tests/handlers/test_register.py b/tests/handlers/test_register.py
index 02111d5d7ff2..312c03c83d70 100644
--- a/tests/handlers/test_register.py
+++ b/tests/handlers/test_register.py
@@ -110,7 +110,7 @@ def test_mau_limits_when_disabled(self):
     def test_get_or_create_user_mau_not_blocked(self):
         self.hs.config.limit_usage_by_mau = True
         self.store.count_monthly_users = Mock(
-            side_effect=lambda: make_awaitable(self.hs.config.max_mau_value - 1)
+            return_value=make_awaitable(self.hs.config.max_mau_value - 1)
         )
         # Ensure does not throw exception
         self.get_success(self.get_or_create_user(self.requester, "c", "User"))
@@ -118,7 +118,7 @@ def test_get_or_create_user_mau_not_blocked(self):
     def test_get_or_create_user_mau_blocked(self):
         self.hs.config.limit_usage_by_mau = True
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.lots_of_users)
+            return_value=make_awaitable(self.lots_of_users)
         )
         self.get_failure(
             self.get_or_create_user(self.requester, "b", "display_name"),
@@ -126,7 +126,7 @@ def test_get_or_create_user_mau_blocked(self):
         )
 
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.hs.config.max_mau_value)
+            return_value=make_awaitable(self.hs.config.max_mau_value)
         )
         self.get_failure(
             self.get_or_create_user(self.requester, "b", "display_name"),
@@ -136,14 +136,14 @@ def test_get_or_create_user_mau_blocked(self):
     def test_register_mau_blocked(self):
         self.hs.config.limit_usage_by_mau = True
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.lots_of_users)
+            return_value=make_awaitable(self.lots_of_users)
         )
         self.get_failure(
             self.handler.register_user(localpart="local_part"), ResourceLimitError
         )
 
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.hs.config.max_mau_value)
+            return_value=make_awaitable(self.hs.config.max_mau_value)
         )
         self.get_failure(
             self.handler.register_user(localpart="local_part"), ResourceLimitError
diff --git a/tests/handlers/test_stats.py b/tests/handlers/test_stats.py
index fba459d32e07..0229f58315be 100644
--- a/tests/handlers/test_stats.py
+++ b/tests/handlers/test_stats.py
@@ -60,7 +60,7 @@ def _add_background_updates(self):
             self.store.db_pool.simple_insert(
                 "background_updates",
                 {
-                    "update_name": "populate_stats_process_rooms_2",
+                    "update_name": "populate_stats_process_rooms",
                     "progress_json": "{}",
                     "depends_on": "populate_stats_prepare",
                 },
@@ -72,7 +72,7 @@ def _add_background_updates(self):
                 {
                     "update_name": "populate_stats_process_users",
                     "progress_json": "{}",
-                    "depends_on": "populate_stats_process_rooms_2",
+                    "depends_on": "populate_stats_process_rooms",
                 },
             )
         )
@@ -225,10 +225,7 @@ def test_initial_earliest_token(self):
         self.get_success(
             self.store.db_pool.simple_insert(
                 "background_updates",
-                {
-                    "update_name": "populate_stats_process_rooms_2",
-                    "progress_json": "{}",
-                },
+                {"update_name": "populate_stats_process_rooms", "progress_json": "{}"},
             )
         )
         self.get_success(
@@ -237,7 +234,7 @@ def test_initial_earliest_token(self):
                 {
                     "update_name": "populate_stats_cleanup",
                     "progress_json": "{}",
-                    "depends_on": "populate_stats_process_rooms_2",
+                    "depends_on": "populate_stats_process_rooms",
                 },
             )
         )
@@ -734,7 +731,7 @@ def test_incomplete_stats(self):
             self.store.db_pool.simple_insert(
                 "background_updates",
                 {
-                    "update_name": "populate_stats_process_rooms_2",
+                    "update_name": "populate_stats_process_rooms",
                     "progress_json": "{}",
                     "depends_on": "populate_stats_prepare",
                 },
@@ -746,7 +743,7 @@ def test_incomplete_stats(self):
                 {
                     "update_name": "populate_stats_process_users",
                     "progress_json": "{}",
-                    "depends_on": "populate_stats_process_rooms_2",
+                    "depends_on": "populate_stats_process_rooms",
                 },
             )
         )
diff --git a/tests/handlers/test_typing.py b/tests/handlers/test_typing.py
index 7bf15c4ba93f..ae6bc24f4cbb 100644
--- a/tests/handlers/test_typing.py
+++ b/tests/handlers/test_typing.py
@@ -116,7 +116,7 @@ def prepare(self, reactor, clock, hs):
             retry_timings_res
         )
 
-        self.datastore.get_device_updates_by_remote.side_effect = lambda destination, from_stream_id, limit: make_awaitable(
+        self.datastore.get_device_updates_by_remote.return_value = make_awaitable(
             (0, [])
         )
 
diff --git a/tests/replication/test_federation_sender_shard.py b/tests/replication/test_federation_sender_shard.py
index 8b4982ecb160..1d7edee5bab3 100644
--- a/tests/replication/test_federation_sender_shard.py
+++ b/tests/replication/test_federation_sender_shard.py
@@ -45,7 +45,7 @@ def test_send_event_single_sender(self):
         new event.
         """
         mock_client = Mock(spec=["put_json"])
-        mock_client.put_json.side_effect = lambda *_, **__: make_awaitable({})
+        mock_client.put_json.return_value = make_awaitable({})
 
         self.make_worker_hs(
             "synapse.app.federation_sender",
@@ -73,7 +73,7 @@ def test_send_event_sharded(self):
         new events.
         """
         mock_client1 = Mock(spec=["put_json"])
-        mock_client1.put_json.side_effect = lambda *_, **__: make_awaitable({})
+        mock_client1.put_json.return_value = make_awaitable({})
         self.make_worker_hs(
             "synapse.app.federation_sender",
             {
@@ -85,7 +85,7 @@ def test_send_event_sharded(self):
         )
 
         mock_client2 = Mock(spec=["put_json"])
-        mock_client2.put_json.side_effect = lambda *_, **__: make_awaitable({})
+        mock_client2.put_json.return_value = make_awaitable({})
         self.make_worker_hs(
             "synapse.app.federation_sender",
             {
@@ -136,7 +136,7 @@ def test_send_typing_sharded(self):
         new typing EDUs.
         """
         mock_client1 = Mock(spec=["put_json"])
-        mock_client1.put_json.side_effect = lambda *_, **__: make_awaitable({})
+        mock_client1.put_json.return_value = make_awaitable({})
         self.make_worker_hs(
             "synapse.app.federation_sender",
             {
@@ -148,7 +148,7 @@ def test_send_typing_sharded(self):
         )
 
         mock_client2 = Mock(spec=["put_json"])
-        mock_client2.put_json.side_effect = lambda *_, **__: make_awaitable({})
+        mock_client2.put_json.return_value = make_awaitable({})
         self.make_worker_hs(
             "synapse.app.federation_sender",
             {
diff --git a/tests/rest/admin/test_user.py b/tests/rest/admin/test_user.py
index 160c63023555..b8b7758d2447 100644
--- a/tests/rest/admin/test_user.py
+++ b/tests/rest/admin/test_user.py
@@ -337,7 +337,7 @@ def test_register_mau_limit_reached(self):
 
         # Set monthly active users to the limit
         store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.hs.config.max_mau_value)
+            return_value=make_awaitable(self.hs.config.max_mau_value)
         )
         # Check that the blocking of monthly active users is working as expected
         # The registration of a new user fails due to the limit
@@ -591,7 +591,7 @@ def test_create_user_mau_limit_reached_active_admin(self):
 
         # Set monthly active users to the limit
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.hs.config.max_mau_value)
+            return_value=make_awaitable(self.hs.config.max_mau_value)
         )
         # Check that the blocking of monthly active users is working as expected
         # The registration of a new user fails due to the limit
@@ -631,7 +631,7 @@ def test_create_user_mau_limit_reached_passive_admin(self):
 
         # Set monthly active users to the limit
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(self.hs.config.max_mau_value)
+            return_value=make_awaitable(self.hs.config.max_mau_value)
         )
         # Check that the blocking of monthly active users is working as expected
         # The registration of a new user fails due to the limit
diff --git a/tests/server_notices/test_resource_limits_server_notices.py b/tests/server_notices/test_resource_limits_server_notices.py
index 973338ea71ad..6382b19dc338 100644
--- a/tests/server_notices/test_resource_limits_server_notices.py
+++ b/tests/server_notices/test_resource_limits_server_notices.py
@@ -67,7 +67,7 @@ def prepare(self, reactor, clock, hs):
             raise Exception("Failed to find reference to ResourceLimitsServerNotices")
 
         self._rlsn._store.user_last_seen_monthly_active = Mock(
-            side_effect=lambda user_id: make_awaitable(1000)
+            return_value=make_awaitable(1000)
         )
         self._rlsn._server_notices_manager.send_notice = Mock(
             return_value=defer.succeed(Mock())
@@ -80,9 +80,7 @@ def prepare(self, reactor, clock, hs):
             return_value=defer.succeed("!something:localhost")
         )
         self._rlsn._store.add_tag_to_room = Mock(return_value=defer.succeed(None))
-        self._rlsn._store.get_tags_for_room = Mock(
-            side_effect=lambda user_id, room_id: make_awaitable({})
-        )
+        self._rlsn._store.get_tags_for_room = Mock(return_value=make_awaitable({}))
 
     @override_config({"hs_disabled": True})
     def test_maybe_send_server_notice_disabled_hs(self):
@@ -158,7 +156,7 @@ def test_maybe_send_server_notice_to_user_not_in_mau_cohort(self):
         """
         self._rlsn._auth.check_auth_blocking = Mock(return_value=defer.succeed(None))
         self._rlsn._store.user_last_seen_monthly_active = Mock(
-            side_effect=lambda user_id: make_awaitable(None)
+            return_value=make_awaitable(None)
         )
         self.get_success(self._rlsn.maybe_send_server_notice_to_user(self.user_id))
 
@@ -261,12 +259,10 @@ def prepare(self, reactor, clock, hs):
         self.user_id = "@user_id:test"
 
     def test_server_notice_only_sent_once(self):
-        self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(1000)
-        )
+        self.store.get_monthly_active_count = Mock(return_value=make_awaitable(1000))
 
         self.store.user_last_seen_monthly_active = Mock(
-            side_effect=lambda user_id: make_awaitable(1000)
+            return_value=make_awaitable(1000)
         )
 
         # Call the function multiple times to ensure we only send the notice once
diff --git a/tests/storage/test_client_ips.py b/tests/storage/test_client_ips.py
index 370c247e16c4..755c70db3142 100644
--- a/tests/storage/test_client_ips.py
+++ b/tests/storage/test_client_ips.py
@@ -154,7 +154,7 @@ def test_adding_monthly_active_user_when_full(self):
         user_id = "@user:server"
 
         self.store.get_monthly_active_count = Mock(
-            side_effect=lambda: make_awaitable(lots_of_users)
+            return_value=make_awaitable(lots_of_users)
         )
         self.get_success(
             self.store.insert_client_ip(
diff --git a/tests/storage/test_monthly_active_users.py b/tests/storage/test_monthly_active_users.py
index 9870c748834f..643072bbaf18 100644
--- a/tests/storage/test_monthly_active_users.py
+++ b/tests/storage/test_monthly_active_users.py
@@ -231,9 +231,7 @@ def test_populate_monthly_users_is_guest(self):
         )
         self.get_success(d)
 
-        self.store.upsert_monthly_active_user = Mock(
-            side_effect=lambda user_id: make_awaitable(None)
-        )
+        self.store.upsert_monthly_active_user = Mock(return_value=make_awaitable(None))
 
         d = self.store.populate_monthly_active_users(user_id)
         self.get_success(d)
@@ -241,9 +239,7 @@ def test_populate_monthly_users_is_guest(self):
         self.store.upsert_monthly_active_user.assert_not_called()
 
     def test_populate_monthly_users_should_update(self):
-        self.store.upsert_monthly_active_user = Mock(
-            side_effect=lambda user_id: make_awaitable(None)
-        )
+        self.store.upsert_monthly_active_user = Mock(return_value=make_awaitable(None))
 
         self.store.is_trial_user = Mock(return_value=defer.succeed(False))
 
@@ -256,9 +252,7 @@ def test_populate_monthly_users_should_update(self):
         self.store.upsert_monthly_active_user.assert_called_once()
 
     def test_populate_monthly_users_should_not_update(self):
-        self.store.upsert_monthly_active_user = Mock(
-            side_effect=lambda user_id: make_awaitable(None)
-        )
+        self.store.upsert_monthly_active_user = Mock(return_value=make_awaitable(None))
 
         self.store.is_trial_user = Mock(return_value=defer.succeed(False))
         self.store.user_last_seen_monthly_active = Mock(
@@ -344,9 +338,7 @@ def test_track_monthly_users_without_cap(self):
 
     @override_config({"limit_usage_by_mau": False, "mau_stats_only": False})
     def test_no_users_when_not_tracking(self):
-        self.store.upsert_monthly_active_user = Mock(
-            side_effect=lambda user_id: make_awaitable(None)
-        )
+        self.store.upsert_monthly_active_user = Mock(return_value=make_awaitable(None))
 
         self.get_success(self.store.populate_monthly_active_users("@user:sever"))
 
diff --git a/tests/test_utils/__init__.py b/tests/test_utils/__init__.py
index 508aeba07826..a298cc0fd330 100644
--- a/tests/test_utils/__init__.py
+++ b/tests/test_utils/__init__.py
@@ -17,6 +17,7 @@
 """
 Utilities for running the unit tests
 """
+from asyncio import Future
 from typing import Any, Awaitable, TypeVar
 
 TV = TypeVar("TV")
@@ -38,6 +39,12 @@ def get_awaitable_result(awaitable: Awaitable[TV]) -> TV:
     raise Exception("awaitable has not yet completed")
 
 
-async def make_awaitable(result: Any):
-    """Create an awaitable that just returns a result."""
-    return result
+def make_awaitable(result: Any) -> Awaitable[Any]:
+    """
+    Makes an awaitable, suitable for mocking an `async` function.
+    This uses Futures as they can be awaited multiple times so can be returned
+    to multiple callers.
+    """
+    future = Future()  # type: ignore
+    future.set_result(result)
+    return future