diff --git a/trio/_sync.py b/trio/_sync.py
index 67438375a7..5a95dc366c 100644
--- a/trio/_sync.py
+++ b/trio/_sync.py
@@ -787,7 +787,7 @@ def statistics(self):
 
 
 @attr.s
-class EventStream:
+class EventStream(metaclass=Final):
     """A concurrency primitive for a sequence of events.
 
     Multiple tasks can subscribe for events on the stream using an ``async