diff --git a/backend/dev_homeserver.yaml b/backend/dev_homeserver.yaml
index b41de45b..b1800b59 100644
--- a/backend/dev_homeserver.yaml
+++ b/backend/dev_homeserver.yaml
@@ -25,6 +25,9 @@ trusted_key_servers:
 experimental_features:
   # MSC3266: Room summary API. Used for knocking over federation
   msc3266_enabled: true
+  # MSC4222 needed for syncv2 state_after. This allow clients to 
+  # correctly track the state of the room.
+  msc4222_enabled: true
 
 # The maximum allowed duration by which sent events can be delayed, as
 # per MSC4140. Must be a positive value if set.  Defaults to no