diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializer.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializer.scala
index 0ac0a2ff40..dd86e2fd01 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializer.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializer.scala
@@ -267,7 +267,7 @@ class ReplicatorMessageSerializer(val system: ExtendedActorSystem)
       case (key, digest) =>
         b.addEntries(dm.Status.Entry.newBuilder().setKey(key).setDigest(ByteString.copyFrom(digest.toArray)))
     }
-    b.setToSystemUid(status.toSystemUid.get)
+    status.toSystemUid.foreach(b.setToSystemUid) // can be None when sending back to a node of version 2.5.21
     b.setFromSystemUid(status.fromSystemUid.get)
     b.build()
   }
@@ -290,7 +290,7 @@ class ReplicatorMessageSerializer(val system: ExtendedActorSystem)
       case (key, data) =>
         b.addEntries(dm.Gossip.Entry.newBuilder().setKey(key).setEnvelope(dataEnvelopeToProto(data)))
     }
-    b.setToSystemUid(gossip.toSystemUid.get)
+    gossip.toSystemUid.foreach(b.setToSystemUid) // can be None when sending back to a node of version 2.5.21
     b.setFromSystemUid(gossip.fromSystemUid.get)
     b.build()
   }
diff --git a/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializerSpec.scala b/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializerSpec.scala
index 86675f9f35..b140d9ba49 100644
--- a/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializerSpec.scala
+++ b/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatorMessageSerializerSpec.scala
@@ -117,12 +117,25 @@ class ReplicatorMessageSerializerSpec
           totChunks = 10,
           Some(17),
           Some(19)))
+      checkSerialization(
+        Status(
+          Map("A" -> ByteString.fromString("a"), "B" → ByteString.fromString("b")),
+          chunk = 3,
+          totChunks = 10,
+          None, // can be None when sending back to a node of version 2.5.21
+          Some(19)))
       checkSerialization(
         Gossip(
           Map("A" -> DataEnvelope(data1), "B" → DataEnvelope(GSet() + "b" + "c")),
           sendBack = true,
           Some(17),
           Some(19)))
+      checkSerialization(
+        Gossip(
+          Map("A" -> DataEnvelope(data1), "B" → DataEnvelope(GSet() + "b" + "c")),
+          sendBack = true,
+          None, // can be None when sending back to a node of version 2.5.21
+          Some(19)))
       checkSerialization(
         DeltaPropagation(
           address1,