1 files changed, 1 insertions, 4 deletions
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 7db6905c61..47a63005a9 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1102,10 +1102,7 @@ class EventCreationHandler:
                 raise SynapseError(400, "Can't send same reaction twice")
 
         # Don't attempt to start a thread if the parent event is a relation.
-        elif (
-            relation_type == RelationTypes.THREAD
-            or relation_type == RelationTypes.UNSTABLE_THREAD
-        ):
+        elif relation_type == RelationTypes.THREAD:
             if await self.store.event_includes_relation(relates_to):
                 raise SynapseError(
                     400, "Cannot start threads from an event with a relation"