diff --git a/synapse/app/generic_worker.py b/synapse/app/generic_worker.py

index 236d98a29d..207d5ccd02 100644
--- a/synapse/app/generic_worker.py
+++ b/synapse/app/generic_worker.py
@@ -302,6 +302,8 @@ class GenericWorkerPresence(BasePresenceHandler):
             self.send_stop_syncing, UPDATE_SYNCING_USERS_MS
         )
 
+        self._busy_presence_enabled = hs.config.experimental.msc3026_enabled
+
         hs.get_reactor().addSystemEventTrigger(
             "before",
             "shutdown",
@@ -439,8 +441,11 @@ class GenericWorkerPresence(BasePresenceHandler):
             PresenceState.ONLINE,
             PresenceState.UNAVAILABLE,
             PresenceState.OFFLINE,
-            PresenceState.BUSY,
         )
+
+        if self._busy_presence_enabled:
+            valid_presence += (PresenceState.BUSY,)
+
         if presence not in valid_presence:
             raise SynapseError(400, "Invalid presence state")