diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/GSet.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/GSet.scala
index 589b9c91d9..4c577449e8 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/GSet.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/GSet.scala
@@ -60,7 +60,7 @@ final case class GSet[A](elements: Set[A]) extends ReplicatedData with Replicate
     else if (this.isAncestorOf(that)) that.clearAncestor()
     else {
       clearAncestor()
-      copy(elements ++ that.elements)
+      copy(elements union that.elements)
     }
 }
 
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 eb6e3d8988..3bb45bebfe 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
@@ -10,8 +10,6 @@ import akka.cluster.Cluster
 import akka.cluster.UniqueAddress
 import akka.util.HashCode
 
-// TODO this class can be optimized, but I wanted to start with correct functionality and comparability with riak_dt_orswot
-
 object ORSet {
   private val _empty: ORSet[Any] = new ORSet(Map.empty, VersionVector.empty)
   def empty[A]: ORSet[A] = _empty.asInstanceOf[ORSet[A]]
diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/PruningState.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/PruningState.scala
index 121b1de5cc..2328c3a9a7 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/PruningState.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/PruningState.scala
@@ -28,7 +28,7 @@ private[akka] final case class PruningState(owner: UniqueAddress, phase: Pruning
       case (_, PruningPerformed) ⇒ that
       case (PruningInitialized(thisSeen), PruningInitialized(thatSeen)) ⇒
         if (this.owner == that.owner)
-          copy(phase = PruningInitialized(thisSeen ++ thatSeen))
+          copy(phase = PruningInitialized(thisSeen union thatSeen))
         else if (Member.addressOrdering.compare(this.owner.address, that.owner.address) > 0)
           that
         else
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 9d3f912f76..2b94d51c0f 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
@@ -1045,7 +1045,7 @@ final class Replicator(settings: ReplicatorSettings) extends Actor with ActorLog
     val myKeys =
       if (totChunks == 1) dataEntries.keySet
       else dataEntries.keysIterator.filter(_.hashCode % totChunks == chunk).toSet
-    val otherMissingKeys = myKeys -- otherKeys
+    val otherMissingKeys = myKeys diff otherKeys
     val keys = (otherDifferentKeys ++ otherMissingKeys).take(maxDeltaElements)
     if (keys.nonEmpty) {
       if (log.isDebugEnabled)
@@ -1053,7 +1053,7 @@ final class Replicator(settings: ReplicatorSettings) extends Actor with ActorLog
       val g = Gossip(keys.map(k ⇒ k -> getData(k).get)(collection.breakOut), sendBack = otherDifferentKeys.nonEmpty)
       sender() ! g
     }
-    val myMissingKeys = otherKeys -- myKeys
+    val myMissingKeys = otherKeys diff myKeys
     if (myMissingKeys.nonEmpty) {
       if (log.isDebugEnabled)
         log.debug("Sending gossip status to [{}], requesting missing [{}]", sender().path.address, myMissingKeys.mkString(", "))