diff --git a/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala b/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala
index 6410a544a3..fb2f3a6430 100644
--- a/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala
+++ b/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala
@@ -402,6 +402,7 @@ object DistributedPubSubMediator {
      */
     def wrapIfNeeded: Any ⇒ Any = {
       case msg: RouterEnvelope ⇒ MediatorRouterEnvelope(msg)
+      case null                ⇒ throw InvalidMessageException("Message must not be null")
       case msg: Any            ⇒ msg
     }
   }