diff --git a/changelog.d/5379.feature b/changelog.d/5379.feature
new file mode 100644
index 0000000000..7b64786fe6
--- /dev/null
+++ b/changelog.d/5379.feature
@@ -0,0 +1 @@
+Set default room version to v4.
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index ea73306fb9..4d7e6f3eb5 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -91,7 +91,7 @@ pid_file: DATADIR/homeserver.pid
 # For example, for room version 1, default_room_version should be set
 # to "1".
 #
-#default_room_version: "1"
+#default_room_version: "4"
 
 # The GC threshold parameters to pass to `gc.set_threshold`, if defined
 #
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 334921d421..7d56e2d141 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -36,7 +36,7 @@ logger = logging.Logger(__name__)
 # in the list.
 DEFAULT_BIND_ADDRESSES = ['::', '0.0.0.0']
 
-DEFAULT_ROOM_VERSION = "1"
+DEFAULT_ROOM_VERSION = "4"
 
 
 class ServerConfig(Config):
diff --git a/tests/storage/test_cleanup_extrems.py b/tests/storage/test_cleanup_extrems.py
index 6dda66ecd3..6aa8b8b3c6 100644
--- a/tests/storage/test_cleanup_extrems.py
+++ b/tests/storage/test_cleanup_extrems.py
@@ -25,6 +25,11 @@ from tests.unittest import HomeserverTestCase
 class CleanupExtremBackgroundUpdateStoreTestCase(HomeserverTestCase):
     """Test the background update to clean forward extremities table.
     """
+    def make_homeserver(self, reactor, clock):
+        # Hack until we understand why test_forked_graph_cleanup fails with v4
+        config = self.default_config()
+        config['default_room_version'] = '1'
+        return self.setup_test_homeserver(config=config)
 
     def prepare(self, reactor, clock, homeserver):
         self.store = homeserver.get_datastore()
@@ -220,6 +225,7 @@ class CleanupExtremBackgroundUpdateStoreTestCase(HomeserverTestCase):
         Where SF* are soft failed, and with them A, B and C marked as
         extremities. This should resolve to B and C being marked as extremity.
         """
+
         # Create the room graph
         event_id_a = self.create_and_send_event()
         event_id_b = self.create_and_send_event()
diff --git a/tests/utils.py b/tests/utils.py
index b2817cf22c..f8c7ad2604 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -31,6 +31,7 @@ from synapse.api.constants import EventTypes
 from synapse.api.errors import CodeMessageException, cs_error
 from synapse.api.room_versions import RoomVersions
 from synapse.config.homeserver import HomeServerConfig
+from synapse.config.server import DEFAULT_ROOM_VERSION
 from synapse.federation.transport import server as federation_server
 from synapse.http.server import HttpServer
 from synapse.server import HomeServer
@@ -173,7 +174,7 @@ def default_config(name, parse=False):
         "use_frozen_dicts": False,
         # We need a sane default_room_version, otherwise attempts to create
         # rooms will fail.
-        "default_room_version": "1",
+        "default_room_version": DEFAULT_ROOM_VERSION,
         # disable user directory updates, because they get done in the
         # background, which upsets the test runner.
         "update_user_directory": False,