diff --git a/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMediatorSpec.cs b/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMediatorSpec.cs
index 59de9952e4b..68650903905 100644
--- a/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMediatorSpec.cs
+++ b/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMediatorSpec.cs
@@ -15,6 +15,7 @@
 
 namespace Akka.Cluster.Tools.Tests.PublishSubscribe
 {
+    [Collection(nameof(DistributedPubSubMediatorSpec))]
     public class DistributedPubSubMediatorSpec : AkkaSpec
     {
         public DistributedPubSubMediatorSpec() : base(GetConfig()) { }
diff --git a/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMessageSerializerSpec.cs b/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMessageSerializerSpec.cs
index 420f21e2fac..fcc0b425f17 100644
--- a/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMessageSerializerSpec.cs
+++ b/src/contrib/cluster/Akka.Cluster.Tools.Tests/PublishSubscribe/DistributedPubSubMessageSerializerSpec.cs
@@ -17,6 +17,7 @@
 
 namespace Akka.Cluster.Tools.Tests.PublishSubscribe
 {
+    [Collection(nameof(DistributedPubSubMessageSerializerSpec))]
     public class DistributedPubSubMessageSerializerSpec : AkkaSpec
     {
         public DistributedPubSubMessageSerializerSpec()