diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/Replicator.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/Replicator.scala
index 5321328caf..ad359066f4 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/Replicator.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/Replicator.scala
@@ -857,9 +857,10 @@ final class Replicator(settings: ReplicatorSettings) extends Actor with ActorLog
     val localValue = getData(key.id)
     Try {
       localValue match {
-        case Some(DataEnvelope(DeletedData, _))         ⇒ throw new DataDeleted(key)
-        case Some(envelope @ DataEnvelope(existing, _)) ⇒ modify(Some(existing))
-        case None                                       ⇒ modify(None)
+        case Some(DataEnvelope(DeletedData, _)) ⇒ throw new DataDeleted(key)
+        case Some(envelope @ DataEnvelope(existing, _)) ⇒
+          existing.merge(modify(Some(existing)).asInstanceOf[existing.T])
+        case None ⇒ modify(None)
       }
     } match {
       case Success(newData) ⇒
diff --git a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorSpec.scala b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorSpec.scala
index 8872e53dab..00a250c0d1 100644
--- a/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorSpec.scala
+++ b/akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorSpec.scala
@@ -59,10 +59,17 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
   val KeyG = ORSetKey[String]("G")
   val KeyH = ORMapKey[Flag]("H")
   val KeyI = GSetKey[String]("I")
+  val KeyJ = GSetKey[String]("J")
   val KeyX = GCounterKey("X")
   val KeyY = GCounterKey("Y")
   val KeyZ = GCounterKey("Z")
 
+  var afterCounter = 0
+  def enterBarrierAfterTestStep(): Unit = {
+    afterCounter += 1
+    enterBarrier("after-" + afterCounter)
+  }
+
   def join(from: RoleName, to: RoleName): Unit = {
     runOn(from) {
       cluster join node(to).address
@@ -145,10 +152,24 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
         expectMsg(GetKeyIdsResult(Set("A")))
       }
 
-      enterBarrier("after-1")
+      enterBarrierAfterTestStep()
     }
   }
 
+  "merge the update with existing value" in {
+    runOn(first) {
+      // in case user is not using the passed in existing value
+      replicator ! Update(KeyJ, GSet(), WriteLocal)(_ + "a" + "b")
+      expectMsg(UpdateSuccess(KeyJ, None))
+      replicator ! Update(KeyJ, GSet(), WriteLocal)(_ ⇒ GSet.empty[String] + "c") // normal usage would be `_ + "c"`
+      expectMsg(UpdateSuccess(KeyJ, None))
+      replicator ! Get(KeyJ, ReadLocal)
+      val s = expectMsgPF() { case g @ GetSuccess(KeyJ, _) ⇒ g.get(KeyJ) }
+      s should ===(GSet.empty[String] + "a" + "b" + "c")
+    }
+    enterBarrierAfterTestStep()
+  }
+
   "reply with ModifyFailure if exception is thrown by modify function" in {
     val e = new RuntimeException("errr")
     replicator ! Update(KeyA, GCounter(), WriteLocal)(_ ⇒ throw e)
@@ -184,7 +205,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       c.value should be(6)
     }
 
-    enterBarrier("after-2")
+    enterBarrierAfterTestStep()
   }
 
   "work in 2 node cluster" in {
@@ -234,7 +255,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       }
     }
 
-    enterBarrier("after-3")
+    enterBarrierAfterTestStep()
   }
 
   "be replicated after succesful update" in {
@@ -309,7 +330,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       }
     }
 
-    enterBarrier("after-4")
+    enterBarrierAfterTestStep()
   }
 
   "converge after partition" in {
@@ -360,7 +381,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       }
     }
 
-    enterBarrier("after-5")
+    enterBarrierAfterTestStep()
   }
 
   "support majority quorum write and read with 3 nodes with 1 unreachable" in {
@@ -463,7 +484,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       c155.value should be(155)
     }
 
-    enterBarrier("after-6")
+    enterBarrierAfterTestStep()
   }
 
   "converge after many concurrent updates" in within(10.seconds) {
@@ -482,7 +503,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       val c = expectMsgPF() { case g @ GetSuccess(KeyF, _) ⇒ g.get(KeyF) }
       c.value should be(3 * 100)
     }
-    enterBarrier("after-7")
+    enterBarrierAfterTestStep()
   }
 
   "read-repair happens before GetSuccess" in {
@@ -497,7 +518,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
       replicator ! Get(KeyG, ReadLocal)
       expectMsgPF() { case g @ GetSuccess(KeyG, _) ⇒ g.get(KeyG).elements } should be(Set("a", "b"))
     }
-    enterBarrier("after-8")
+    enterBarrierAfterTestStep()
   }
 
   "check that a remote update and a local update both cause a change event to emit with the merged data" in {
@@ -523,7 +544,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
         Map("a" -> Flag(enabled = true), "b" -> Flag(enabled = true)))
     }
 
-    enterBarrier("after-9")
+    enterBarrierAfterTestStep()
   }
 
   "avoid duplicate change events for same data" in {
@@ -547,7 +568,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
 
     changedProbe.expectNoMsg(1.second)
 
-    enterBarrier("after-10")
+    enterBarrierAfterTestStep()
   }
 
 }