diff --git a/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala b/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
index 3adbbae324..ff954a83cf 100644
--- a/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
@@ -75,7 +75,7 @@ private[cluster] object InternalClusterAction {
   /**
    * Marker interface for periodic tick messages
    */
-  trait Tick
+  sealed trait Tick
 
   case object GossipTick extends Tick