diff --git a/changelog.d/6220.feature b/changelog.d/6220.feature
new file mode 100644
index 000000000..8343e9912
--- /dev/null
+++ b/changelog.d/6220.feature
@@ -0,0 +1 @@
+Increase default room version from 4 to 5, thereby enforcing server key validity period checks.
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index d2f4aff82..35b0bdf6f 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -72,7 +72,7 @@ pid_file: DATADIR/homeserver.pid
 # For example, for room version 1, default_room_version should be set
 # to "1".
 #
-#default_room_version: "4"
+#default_room_version: "5"
 
 # 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 d556df308..9015ca5f8 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -41,7 +41,7 @@ logger = logging.Logger(__name__)
 # in the list.
 DEFAULT_BIND_ADDRESSES = ["::", "0.0.0.0"]
 
-DEFAULT_ROOM_VERSION = "4"
+DEFAULT_ROOM_VERSION = "5"
 
 ROOM_COMPLEXITY_TOO_GREAT = (
     "Your homeserver is unable to join rooms this large or complex. "