diff --git a/akka-distributed-data/src/main/java/akka/cluster/ddata/protobuf/msg/ReplicatedDataMessages.java b/akka-distributed-data/src/main/java/akka/cluster/ddata/protobuf/msg/ReplicatedDataMessages.java
index 1f25776e93..2cbf071334 100644
--- a/akka-distributed-data/src/main/java/akka/cluster/ddata/protobuf/msg/ReplicatedDataMessages.java
+++ b/akka-distributed-data/src/main/java/akka/cluster/ddata/protobuf/msg/ReplicatedDataMessages.java
@@ -9846,17 +9846,17 @@ public final class ReplicatedDataMessages {
       akka.protobuf.ByteString
           getStringKeyBytes();
 
-      // required .akka.cluster.ddata.OtherMessage value = 2;
+      // optional .akka.cluster.ddata.OtherMessage value = 2;
       /**
-       * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+       * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
        */
       boolean hasValue();
       /**
-       * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+       * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
        */
       akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage getValue();
       /**
-       * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+       * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
        */
       akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessageOrBuilder getValueOrBuilder();
 
@@ -10069,23 +10069,23 @@ public final class ReplicatedDataMessages {
         }
       }
 
-      // required .akka.cluster.ddata.OtherMessage value = 2;
+      // optional .akka.cluster.ddata.OtherMessage value = 2;
       public static final int VALUE_FIELD_NUMBER = 2;
       private akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage value_;
       /**
-       * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+       * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
        */
       public boolean hasValue() {
         return ((bitField0_ & 0x00000002) == 0x00000002);
       }
       /**
-       * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+       * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
        */
       public akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage getValue() {
         return value_;
       }
       /**
-       * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+       * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
        */
       public akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessageOrBuilder getValueOrBuilder() {
         return value_;
@@ -10157,13 +10157,11 @@ public final class ReplicatedDataMessages {
         byte isInitialized = memoizedIsInitialized;
         if (isInitialized != -1) return isInitialized == 1;
 
-        if (!hasValue()) {
-          memoizedIsInitialized = 0;
-          return false;
-        }
-        if (!getValue().isInitialized()) {
-          memoizedIsInitialized = 0;
-          return false;
+        if (hasValue()) {
+          if (!getValue().isInitialized()) {
+            memoizedIsInitialized = 0;
+            return false;
+          }
         }
         if (hasOtherKey()) {
           if (!getOtherKey().isInitialized()) {
@@ -10452,13 +10450,11 @@ public final class ReplicatedDataMessages {
         }
 
         public final boolean isInitialized() {
-          if (!hasValue()) {
-            
-            return false;
-          }
-          if (!getValue().isInitialized()) {
-            
-            return false;
+          if (hasValue()) {
+            if (!getValue().isInitialized()) {
+              
+              return false;
+            }
           }
           if (hasOtherKey()) {
             if (!getOtherKey().isInitialized()) {
@@ -10562,18 +10558,18 @@ public final class ReplicatedDataMessages {
           return this;
         }
 
-        // required .akka.cluster.ddata.OtherMessage value = 2;
+        // optional .akka.cluster.ddata.OtherMessage value = 2;
         private akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage value_ = akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage.getDefaultInstance();
         private akka.protobuf.SingleFieldBuilder<
             akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage, akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage.Builder, akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessageOrBuilder> valueBuilder_;
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public boolean hasValue() {
           return ((bitField0_ & 0x00000002) == 0x00000002);
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage getValue() {
           if (valueBuilder_ == null) {
@@ -10583,7 +10579,7 @@ public final class ReplicatedDataMessages {
           }
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public Builder setValue(akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage value) {
           if (valueBuilder_ == null) {
@@ -10599,7 +10595,7 @@ public final class ReplicatedDataMessages {
           return this;
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public Builder setValue(
             akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage.Builder builderForValue) {
@@ -10613,7 +10609,7 @@ public final class ReplicatedDataMessages {
           return this;
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public Builder mergeValue(akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage value) {
           if (valueBuilder_ == null) {
@@ -10632,7 +10628,7 @@ public final class ReplicatedDataMessages {
           return this;
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public Builder clearValue() {
           if (valueBuilder_ == null) {
@@ -10645,7 +10641,7 @@ public final class ReplicatedDataMessages {
           return this;
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage.Builder getValueBuilder() {
           bitField0_ |= 0x00000002;
@@ -10653,7 +10649,7 @@ public final class ReplicatedDataMessages {
           return getValueFieldBuilder().getBuilder();
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         public akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessageOrBuilder getValueOrBuilder() {
           if (valueBuilder_ != null) {
@@ -10663,7 +10659,7 @@ public final class ReplicatedDataMessages {
           }
         }
         /**
-         * <code>required .akka.cluster.ddata.OtherMessage value = 2;</code>
+         * <code>optional .akka.cluster.ddata.OtherMessage value = 2;</code>
          */
         private akka.protobuf.SingleFieldBuilder<
             akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage, akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessage.Builder, akka.cluster.ddata.protobuf.msg.ReplicatorMessages.OtherMessageOrBuilder> 
@@ -18396,7 +18392,7 @@ public final class ReplicatedDataMessages {
       "age\"\263\003\n\017ORMapDeltaGroup\022:\n\007entries\030\001 \003(\013" +
       "2).akka.cluster.ddata.ORMapDeltaGroup.En" +
       "try\032\243\001\n\010MapEntry\022\021\n\tstringKey\030\001 \001(\t\022/\n\005v" +
-      "alue\030\002 \002(\0132 .akka.cluster.ddata.OtherMes" +
+      "alue\030\002 \001(\0132 .akka.cluster.ddata.OtherMes" +
       "sage\022\016\n\006intKey\030\003 \001(\021\022\017\n\007longKey\030\004 \001(\022\0222\n" +
       "\010otherKey\030\005 \001(\0132 .akka.cluster.ddata.Oth" +
       "erMessage\032\275\001\n\005Entry\0223\n\toperation\030\001 \002(\0162 ",
diff --git a/akka-distributed-data/src/main/protobuf/ReplicatedDataMessages.proto b/akka-distributed-data/src/main/protobuf/ReplicatedDataMessages.proto
index 33efe55f5a..ca6b2fbdca 100644
--- a/akka-distributed-data/src/main/protobuf/ReplicatedDataMessages.proto
+++ b/akka-distributed-data/src/main/protobuf/ReplicatedDataMessages.proto
@@ -78,7 +78,7 @@ message ORMap {
 message ORMapDeltaGroup {
   message MapEntry {
     optional string stringKey = 1;
-    required OtherMessage value = 2;
+    optional OtherMessage value = 2;
     optional sint32 intKey = 3;
     optional sint64 longKey = 4;
     optional OtherMessage otherKey = 5;
diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORMap.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORMap.scala
index 1240e7fdbd..b8336f2239 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORMap.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORMap.scala
@@ -25,7 +25,7 @@ object ORMap {
    */
   def unapply[A, B <: ReplicatedData](m: ORMap[A, B]): Option[Map[A, B]] = Some(m.entries)
 
-  sealed trait DeltaOp extends ReplicatedDelta with RequiresCausalDeliveryOfDeltas {
+  sealed trait DeltaOp extends ReplicatedDelta with RequiresCausalDeliveryOfDeltas with ReplicatedDataSerialization {
     type T = DeltaOp
     override def zero: DeltaReplicatedData
   }
diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORSet.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORSet.scala
index fa3eacd744..7f449ccfee 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORSet.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/ORSet.scala
@@ -38,7 +38,7 @@ object ORSet {
    */
   @InternalApi private[akka]type Dot = VersionVector
 
-  sealed trait DeltaOp extends ReplicatedDelta with RequiresCausalDeliveryOfDeltas {
+  sealed trait DeltaOp extends ReplicatedDelta with RequiresCausalDeliveryOfDeltas with ReplicatedDataSerialization {
     type T = DeltaOp
   }
 
diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializer.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializer.scala
index cd9eff03b5..8d713e4633 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializer.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializer.scala
@@ -585,6 +585,13 @@ class ReplicatedDataSerializer(val system: ExtendedActorSystem)
     }
   }
 
+  def singleKeyEntryFromProto[PEntry <: GeneratedMessage, A <: GeneratedMessage](entry: PEntry)(implicit eh: ProtoMapEntryReader[PEntry, A]): Any =
+    if (eh.hasStringKey(entry)) eh.getStringKey(entry)
+    else if (eh.hasIntKey(entry)) eh.getIntKey(entry)
+    else if (eh.hasLongKey(entry)) eh.getLongKey(entry)
+    else if (eh.hasOtherKey(entry)) otherMessageFromProto(eh.getOtherKey(entry))
+    else throw new IllegalArgumentException(s"Can't deserialize the key in the ORMap delta")
+
   // wire protocol is always DeltaGroup
   private def ormapPutFromBinary(bytes: Array[Byte]): ORMap.PutDeltaOp[Any, ReplicatedData] = {
     val group = ormapDeltaGroupFromBinary(bytes)
@@ -639,11 +646,10 @@ class ReplicatedDataSerializer(val system: ExtendedActorSystem)
           val map = singleMapEntryFromProto(entry.getEntryData, (v: dm.OtherMessage) ⇒ otherMessageFromProto(v).asInstanceOf[ReplicatedData])
           ORMap.PutDeltaOp(ORSet.AddDeltaOp(orsetFromProto(entry.getUnderlying)), map.head, zeroTagFromCode(entry.getZeroTag))
         } else if (entry.getOperation == rd.ORMapDeltaOp.ORMapRemove) {
-          val map = singleMapEntryFromProto(entry.getEntryData, (v: dm.OtherMessage) ⇒ otherMessageFromProto(v).asInstanceOf[ReplicatedData])
           ORMap.RemoveDeltaOp(ORSet.RemoveDeltaOp(orsetFromProto(entry.getUnderlying)), zeroTagFromCode(entry.getZeroTag))
         } else if (entry.getOperation == rd.ORMapDeltaOp.ORMapRemoveKey) {
-          val map = singleMapEntryFromProto(entry.getEntryData, (v: dm.OtherMessage) ⇒ otherMessageFromProto(v).asInstanceOf[ReplicatedData])
-          ORMap.RemoveKeyDeltaOp(ORSet.RemoveDeltaOp(orsetFromProto(entry.getUnderlying)), map.keySet.head, zeroTagFromCode(entry.getZeroTag))
+          val elem = singleKeyEntryFromProto(entry.getEntryData)
+          ORMap.RemoveKeyDeltaOp(ORSet.RemoveDeltaOp(orsetFromProto(entry.getUnderlying)), elem, zeroTagFromCode(entry.getZeroTag))
         } else if (entry.getOperation == rd.ORMapDeltaOp.ORMapUpdate) {
           val map = singleMapEntryFromProto(entry.getEntryData, (v: dm.OtherMessage) ⇒ otherMessageFromProto(v).asInstanceOf[ReplicatedDelta])
           ORMap.UpdateDeltaOp(ORSet.AddDeltaOp(orsetFromProto(entry.getUnderlying)), map, zeroTagFromCode(entry.getZeroTag))
@@ -653,20 +659,20 @@ class ReplicatedDataSerializer(val system: ExtendedActorSystem)
     ORMap.DeltaGroup(ops)
   }
 
-  private def ormapPutToProto(addDelta: ORMap.PutDeltaOp[_, _]): rd.ORMapDeltaGroup = {
-    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(addDelta.asInstanceOf[ORMap.DeltaOp])))
+  private def ormapPutToProto(deltaOp: ORMap.PutDeltaOp[_, _]): rd.ORMapDeltaGroup = {
+    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(deltaOp.asInstanceOf[ORMap.DeltaOp])))
   }
 
-  private def ormapRemoveToProto(addDelta: ORMap.RemoveDeltaOp[_, _]): rd.ORMapDeltaGroup = {
-    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(addDelta.asInstanceOf[ORMap.DeltaOp])))
+  private def ormapRemoveToProto(deltaOp: ORMap.RemoveDeltaOp[_, _]): rd.ORMapDeltaGroup = {
+    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(deltaOp.asInstanceOf[ORMap.DeltaOp])))
   }
 
-  private def ormapRemoveKeyToProto(addDelta: ORMap.RemoveKeyDeltaOp[_, _]): rd.ORMapDeltaGroup = {
-    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(addDelta.asInstanceOf[ORMap.DeltaOp])))
+  private def ormapRemoveKeyToProto(deltaOp: ORMap.RemoveKeyDeltaOp[_, _]): rd.ORMapDeltaGroup = {
+    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(deltaOp.asInstanceOf[ORMap.DeltaOp])))
   }
 
-  private def ormapUpdateToProto(addDelta: ORMap.UpdateDeltaOp[_, _]): rd.ORMapDeltaGroup = {
-    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(addDelta.asInstanceOf[ORMap.DeltaOp])))
+  private def ormapUpdateToProto(deltaOp: ORMap.UpdateDeltaOp[_, _]): rd.ORMapDeltaGroup = {
+    ormapDeltaGroupToProto(ORMap.DeltaGroup(scala.collection.immutable.IndexedSeq(deltaOp.asInstanceOf[ORMap.DeltaOp])))
   }
 
   private def ormapDeltaGroupToProto(deltaGroup: ORMap.DeltaGroup[_, _]): rd.ORMapDeltaGroup = {
@@ -691,6 +697,22 @@ class ReplicatedDataSerializer(val system: ExtendedActorSystem)
       }
     }
 
+    def createEntryWithKey(opType: rd.ORMapDeltaOp, u: ORSet[_], k: Any, zt: Int) = {
+      val entryDataBuilder = rd.ORMapDeltaGroup.MapEntry.newBuilder()
+      k match {
+        case key: String ⇒ entryDataBuilder.setStringKey(key)
+        case key: Int    ⇒ entryDataBuilder.setIntKey(key)
+        case key: Long   ⇒ entryDataBuilder.setLongKey(key)
+        case key         ⇒ entryDataBuilder.setOtherKey(otherMessageToProto(key))
+      }
+      val builder = rd.ORMapDeltaGroup.Entry.newBuilder()
+        .setOperation(opType)
+        .setUnderlying(orsetToProto(u))
+        .setZeroTag(zt)
+      builder.setEntryData(entryDataBuilder.build())
+      builder
+    }
+
     val b = rd.ORMapDeltaGroup.newBuilder()
     deltaGroup.ops.foreach {
       case ORMap.PutDeltaOp(op, pair, zt) ⇒
@@ -698,7 +720,7 @@ class ReplicatedDataSerializer(val system: ExtendedActorSystem)
       case ORMap.RemoveDeltaOp(op, zt) ⇒
         b.addEntries(createEntry(rd.ORMapDeltaOp.ORMapRemove, op.asInstanceOf[ORSet.RemoveDeltaOp[_]].underlying, Map.empty, zt.value))
       case ORMap.RemoveKeyDeltaOp(op, k, zt) ⇒
-        b.addEntries(createEntry(rd.ORMapDeltaOp.ORMapRemove, op.asInstanceOf[ORSet.RemoveDeltaOp[_]].underlying, Map(k → k), zt.value))
+        b.addEntries(createEntryWithKey(rd.ORMapDeltaOp.ORMapRemoveKey, op.asInstanceOf[ORSet.RemoveDeltaOp[_]].underlying, k, zt.value))
       case ORMap.UpdateDeltaOp(op, m, zt) ⇒
         b.addEntries(createEntry(rd.ORMapDeltaOp.ORMapUpdate, op.asInstanceOf[ORSet.AddDeltaOp[_]].underlying, m, zt.value))
       case ORMap.DeltaGroup(u) ⇒
diff --git a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorMapDeltaSpec.scala b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorMapDeltaSpec.scala
index f083fdbf30..f0597e79db 100644
--- a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorMapDeltaSpec.scala
+++ b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorMapDeltaSpec.scala
@@ -25,6 +25,11 @@ object ReplicatorMapDeltaSpec extends MultiNodeConfig {
     akka.loglevel = DEBUG
     akka.actor.provider = "cluster"
     akka.log-dead-letters-during-shutdown = off
+    akka.actor {
+      serialize-messages = off
+      serialize-creators = off
+      allow-java-serialization = off
+    }
     """))
 
   testTransport(on = true)
@@ -182,8 +187,8 @@ class ReplicatorMapDeltaSpec extends MultiNodeSpec(ReplicatorMapDeltaSpec) with
           deltaReplicator ! Update(key._1, PNCounterMap.empty[String], WriteLocal)(_ increment key._2)
         }
         List(KeyD, KeyE, KeyF).foreach { key ⇒
-          fullStateReplicator ! Update(key._1, ORMultiMap.emptyWithValueDeltas[String, String], WriteLocal)(_ + (key._2, Set("a")))
-          deltaReplicator ! Update(key._1, ORMultiMap.emptyWithValueDeltas[String, String], WriteLocal)(_ + (key._2, Set("a")))
+          fullStateReplicator ! Update(key._1, ORMultiMap.emptyWithValueDeltas[String, String], WriteLocal)(_ + (key._2 → Set("a")))
+          deltaReplicator ! Update(key._1, ORMultiMap.emptyWithValueDeltas[String, String], WriteLocal)(_ + (key._2 → Set("a")))
         }
       }
       enterBarrier("updated-1")
diff --git a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorORSetDeltaSpec.scala b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorORSetDeltaSpec.scala
index 3d1a9581a8..6925b80044 100644
--- a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorORSetDeltaSpec.scala
+++ b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorORSetDeltaSpec.scala
@@ -22,6 +22,11 @@ object ReplicatorORSetDeltaSpec extends MultiNodeConfig {
     akka.loglevel = INFO
     akka.actor.provider = "cluster"
     akka.log-dead-letters-during-shutdown = off
+    akka.actor {
+      serialize-messages = off
+      serialize-creators = off
+      allow-java-serialization = off
+    }
     """))
 
   testTransport(on = true)
diff --git a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorPruningSpec.scala b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorPruningSpec.scala
index da67a36434..b05bb5fe50 100644
--- a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorPruningSpec.scala
+++ b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorPruningSpec.scala
@@ -91,10 +91,10 @@ class ReplicatorPruningSpec extends MultiNodeSpec(ReplicatorPruningSpec) with ST
       replicator ! Update(KeyC, PNCounterMap.empty[String], WriteAll(timeout)) { _ increment "x" increment "y" }
       expectMsg(UpdateSuccess(KeyC, None))
 
-      replicator ! Update(KeyD, ORMultiMap.empty[String, String], WriteAll(timeout)) { _ + ("a", Set("A")) }
+      replicator ! Update(KeyD, ORMultiMap.empty[String, String], WriteAll(timeout)) { _ + ("a" → Set("A")) }
       expectMsg(UpdateSuccess(KeyD, None))
 
-      replicator ! Update(KeyE, ORMap.empty[String, GSet[String]], WriteAll(timeout)) { _ + ("a", GSet.empty[String].add("A")) }
+      replicator ! Update(KeyE, ORMap.empty[String, GSet[String]], WriteAll(timeout)) { _ + ("a" → GSet.empty[String].add("A")) }
       expectMsg(UpdateSuccess(KeyE, None))
 
       enterBarrier("updates-done")
diff --git a/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializerSpec.scala b/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializerSpec.scala
index b77c363f2b..da86a68dc2 100644
--- a/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializerSpec.scala
+++ b/akka-distributed-data/src/test/scala/akka/cluster/ddata/protobuf/ReplicatedDataSerializerSpec.scala
@@ -17,6 +17,7 @@ import akka.testkit.TestKit
 import akka.cluster.UniqueAddress
 import akka.remote.RARP
 import com.typesafe.config.ConfigFactory
+import akka.actor.Props
 
 class ReplicatedDataSerializerSpec extends TestKit(ActorSystem(
   "ReplicatedDataSerializerSpec",
@@ -24,6 +25,11 @@ class ReplicatedDataSerializerSpec extends TestKit(ActorSystem(
     akka.actor.provider=cluster
     akka.remote.netty.tcp.port=0
     akka.remote.artery.canonical.port = 0
+    akka.actor {
+      serialize-messages = off
+      serialize-creators = off
+      allow-java-serialization = off
+    }
     """))) with WordSpecLike with Matchers with BeforeAndAfterAll {
 
   val serializer = new ReplicatedDataSerializer(system.asInstanceOf[ExtendedActorSystem])
@@ -34,6 +40,10 @@ class ReplicatedDataSerializerSpec extends TestKit(ActorSystem(
   val address2 = UniqueAddress(Address(Protocol, system.name, "other.host.org", 4711), 2L)
   val address3 = UniqueAddress(Address(Protocol, system.name, "some.host.org", 4712), 3L)
 
+  val ref1 = system.actorOf(Props.empty, "ref1")
+  val ref2 = system.actorOf(Props.empty, "ref2")
+  val ref3 = system.actorOf(Props.empty, "ref3")
+
   override def afterAll {
     shutdown()
   }
@@ -71,14 +81,14 @@ class ReplicatedDataSerializerSpec extends TestKit(ActorSystem(
       checkSerialization(GSet() + "a" + "b")
 
       checkSerialization(GSet() + 1 + 2 + 3)
-      checkSerialization(GSet() + address1 + address2)
+      checkSerialization(GSet() + ref1 + ref2)
 
-      checkSerialization(GSet() + 1L + "2" + 3 + address1)
+      checkSerialization(GSet() + 1L + "2" + 3 + ref1)
 
       checkSameContent(GSet() + "a" + "b", GSet() + "a" + "b")
       checkSameContent(GSet() + "a" + "b", GSet() + "b" + "a")
-      checkSameContent(GSet() + address1 + address2 + address3, GSet() + address2 + address1 + address3)
-      checkSameContent(GSet() + address1 + address2 + address3, GSet() + address3 + address2 + address1)
+      checkSameContent(GSet() + ref1 + ref2 + ref3, GSet() + ref2 + ref1 + ref3)
+      checkSameContent(GSet() + ref1 + ref2 + ref3, GSet() + ref3 + ref2 + ref1)
     }
 
     "serialize ORSet" in {
@@ -89,7 +99,7 @@ class ReplicatedDataSerializerSpec extends TestKit(ActorSystem(
       checkSerialization(ORSet().add(address1, "a").add(address2, "b").remove(address1, "a"))
       checkSerialization(ORSet().add(address1, 1).add(address2, 2))
       checkSerialization(ORSet().add(address1, 1L).add(address2, 2L))
-      checkSerialization(ORSet().add(address1, "a").add(address2, 2).add(address3, 3L).add(address3, address3))
+      checkSerialization(ORSet().add(address1, "a").add(address2, 2).add(address3, 3L).add(address3, ref3))
 
       val s1 = ORSet().add(address1, "a").add(address2, "b")
       val s2 = ORSet().add(address2, "b").add(address1, "a")
@@ -267,6 +277,7 @@ class ReplicatedDataSerializerSpec extends TestKit(ActorSystem(
       checkSerialization(ORMultiMap._emptyWithValueDeltas.addBinding(address1, 1, "A"))
       checkSerialization(ORMultiMap._emptyWithValueDeltas.addBinding(address1, 1L, "A"))
       checkSerialization(ORMultiMap._emptyWithValueDeltas.addBinding(address1, Flag(), "A"))
+      checkSerialization(ORMultiMap.emptyWithValueDeltas[String, String].addBinding(address1, "a", "A").remove(address1, "a").delta.get)
       checkSerialization(ORMultiMap.emptyWithValueDeltas[String, String]
         .addBinding(address1, "a", "A1")
         .put(address2, "b", Set("B1", "B2", "B3"))
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 7bec0ef523..22fb7d772a 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
@@ -26,6 +26,8 @@ import com.typesafe.config.ConfigFactory
 import akka.cluster.ddata.DurableStore.DurableDataEnvelope
 import akka.cluster.ddata.GCounter
 import akka.cluster.ddata.VersionVector
+import akka.cluster.ddata.ORSet
+import akka.cluster.ddata.ORMultiMap
 
 class ReplicatorMessageSerializerSpec extends TestKit(ActorSystem(
   "ReplicatorMessageSerializerSpec",
@@ -33,6 +35,11 @@ class ReplicatorMessageSerializerSpec extends TestKit(ActorSystem(
     akka.actor.provider=cluster
     akka.remote.netty.tcp.port=0
     akka.remote.artery.canonical.port = 0
+    akka.actor {
+      serialize-messages = off
+      serialize-creators = off
+      allow-java-serialization = off
+    }
     """))) with WordSpecLike with Matchers with BeforeAndAfterAll {
 
   val serializer = new ReplicatorMessageSerializer(system.asInstanceOf[ExtendedActorSystem])
@@ -61,8 +68,10 @@ class ReplicatorMessageSerializerSpec extends TestKit(ActorSystem(
     "serialize Replicator messages" in {
       val ref1 = system.actorOf(Props.empty, "ref1")
       val data1 = GSet.empty[String] + "a"
-      val delta1 = GCounter.empty.increment(address1, 17).increment(address2, 2)
-      val delta2 = delta1.increment(address2, 1)
+      val delta1 = GCounter.empty.increment(address1, 17).increment(address2, 2).delta.get
+      val delta2 = delta1.increment(address2, 1).delta.get
+      val delta3 = ORSet.empty[String].add(address1, "a").delta.get
+      val delta4 = ORMultiMap.empty[String, String].addBinding(address1, "a", "b").delta.get
 
       checkSerialization(Get(keyA, ReadLocal))
       checkSerialization(Get(keyA, ReadMajority(2.seconds), Some("x")))
@@ -92,7 +101,9 @@ class ReplicatorMessageSerializerSpec extends TestKit(ActorSystem(
         "B" → DataEnvelope(GSet() + "b" + "c")), sendBack = true))
       checkSerialization(DeltaPropagation(address1, reply = true, Map(
         "A" → Delta(DataEnvelope(delta1), 1L, 1L),
-        "B" → Delta(DataEnvelope(delta2), 3L, 5L))))
+        "B" → Delta(DataEnvelope(delta2), 3L, 5L),
+        "C" → Delta(DataEnvelope(delta3), 1L, 1L),
+        "DC" → Delta(DataEnvelope(delta4), 1L, 1L))))
 
       checkSerialization(new DurableDataEnvelope(data1))
       val pruning = Map(