diff --git a/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala b/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
index 1d7a2a7514..2039d8d157 100644
--- a/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
@@ -896,7 +896,7 @@ object ClusterEvent {
   /**
    * Marker interface for cluster domain events.
    */
-  trait ClusterDomainEvent
+  sealed trait ClusterDomainEvent
 
   /**
    * Current snapshot state of the cluster. Sent to new subscriber.