diff --git a/akka-cluster/src/main/scala/akka/cluster/Member.scala b/akka-cluster/src/main/scala/akka/cluster/Member.scala
index dcc7cce527..c5237fb9f7 100644
--- a/akka-cluster/src/main/scala/akka/cluster/Member.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/Member.scala
@@ -53,15 +53,25 @@ class Member private[cluster] (
    * Is this member older, has been part of cluster longer, than another
    * member. It is only correct when comparing two existing members in a
    * cluster. A member that joined after removal of another member may be
-   * considered older than the removed member. Note that is only makes
-   * sense to compare with other members inside of one data center (upNumber has
-   * a higher risk of being reused across data centers). // TODO should we enforce this to compare only within DCs?
+   * considered older than the removed member.
+   *
+   * Note that it only makes sense to compare with other members of
+   * same data center (upNumber has a higher risk of being reused across data centers).
+   * To avoid mistakes of comparing members of different data centers this
+   * method will throw `IllegalArgumentException` if the members belong
+   * to different data centers.
    */
-  def isOlderThan(other: Member): Boolean =
+  @throws[IllegalArgumentException]("if members from different data centers")
+  def isOlderThan(other: Member): Boolean = {
+    if (dataCenter != other.dataCenter)
+      throw new IllegalArgumentException(
+        "Comparing members of different data centers with isOlderThan is not allowed. " +
+          s"[$this] vs. [$other]")
     if (upNumber == other.upNumber)
       Member.addressOrdering.compare(address, other.address) < 0
     else
       upNumber < other.upNumber
+  }
 
   def copy(status: MemberStatus): Member = {
     val oldStatus = this.status
@@ -141,6 +151,11 @@ object Member {
 
   /**
    * Sort members by age, i.e. using [[Member#isOlderThan]].
+   *
+   * Note that it only makes sense to compare with other members of
+   * same data center. To avoid mistakes of comparing members of different
+   * data centers it will throw `IllegalArgumentException` if the
+   * members belong to different data centers.
    */
   val ageOrdering: Ordering[Member] = Ordering.fromLessThan[Member] {
     (a, b) ⇒ a.isOlderThan(b)
diff --git a/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcHeartbeatTakingOverSpec.scala b/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcHeartbeatTakingOverSpec.scala
index 5a3c312da4..3f777d5d61 100644
--- a/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcHeartbeatTakingOverSpec.scala
+++ b/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcHeartbeatTakingOverSpec.scala
@@ -85,10 +85,10 @@ abstract class MultiDcHeartbeatTakingOverSpec extends MultiNodeSpec(MultiDcHeart
     // end of these will be filled in during the initial phase of the test -----------
 
     def refreshOldestMemberHeartbeatStatuses() = {
-      expectedAlphaHeartbeaterNodes = takeNOldestMembers(_.dataCenter == "alpha", 2)
+      expectedAlphaHeartbeaterNodes = takeNOldestMembers(dataCenter = "alpha", 2)
       expectedAlphaHeartbeaterRoles = membersAsRoles(expectedAlphaHeartbeaterNodes)
 
-      expectedBetaHeartbeaterNodes = takeNOldestMembers(_.dataCenter == "beta", 2)
+      expectedBetaHeartbeaterNodes = takeNOldestMembers(dataCenter = "beta", 2)
       expectedBetaHeartbeaterRoles = membersAsRoles(expectedBetaHeartbeaterNodes)
 
       expectedNoActiveHeartbeatSenderRoles = roles.toSet -- (expectedAlphaHeartbeaterRoles union expectedBetaHeartbeaterRoles)
@@ -154,7 +154,7 @@ abstract class MultiDcHeartbeatTakingOverSpec extends MultiNodeSpec(MultiDcHeart
       enterBarrier("after-alpha-monitoring-node-left")
 
       implicit val sender = observer.ref
-      val expectedAlphaMonitoringNodesAfterLeaving = (takeNOldestMembers(_.dataCenter == "alpha", 3).filterNot(_.status == MemberStatus.Exiting))
+      val expectedAlphaMonitoringNodesAfterLeaving = (takeNOldestMembers(dataCenter = "alpha", 3).filterNot(_.status == MemberStatus.Exiting))
       runOn(membersAsRoles(expectedAlphaMonitoringNodesAfterLeaving).toList: _*) {
         awaitAssert({
 
@@ -180,16 +180,15 @@ abstract class MultiDcHeartbeatTakingOverSpec extends MultiNodeSpec(MultiDcHeart
    * strongly guaratnee the order of "oldest" members, as they're linearized by the order in which they become Up
    * (since marking that transition is a Leader action).
    */
-  private def membersByAge(): immutable.SortedSet[Member] =
+  private def membersByAge(dataCenter: ClusterSettings.DataCenter): immutable.SortedSet[Member] =
     SortedSet.empty(Member.ageOrdering)
-      .union(cluster.state.members.filter(m ⇒ m.status != MemberStatus.Joining && m.status != MemberStatus.WeaklyUp))
+      .union(cluster.state.members.filter(m ⇒ m.dataCenter == dataCenter &&
+        m.status != MemberStatus.Joining && m.status != MemberStatus.WeaklyUp))
 
   /** INTERNAL API */
   @InternalApi
-  private[cluster] def takeNOldestMembers(memberFilter: Member ⇒ Boolean, n: Int): immutable.SortedSet[Member] =
-    membersByAge()
-      .filter(memberFilter)
-      .take(n)
+  private[cluster] def takeNOldestMembers(dataCenter: ClusterSettings.DataCenter, n: Int): immutable.SortedSet[Member] =
+    membersByAge(dataCenter).take(n)
 
   private def membersAsRoles(ms: SortedSet[Member]): SortedSet[RoleName] = {
     val res = ms.flatMap(m ⇒ roleName(m.address))
diff --git a/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcSunnyWeatherSpec.scala b/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcSunnyWeatherSpec.scala
index e13f2bc691..9f340f31f9 100644
--- a/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcSunnyWeatherSpec.scala
+++ b/akka-cluster/src/multi-jvm/scala/akka/cluster/MultiDcSunnyWeatherSpec.scala
@@ -76,10 +76,10 @@ abstract class MultiDcSunnyWeatherSpec extends MultiNodeSpec(MultiDcSunnyWeather
       val crossDcHeartbeatSenderPath = "/system/cluster/core/daemon/crossDcHeartbeatSender"
       val selectCrossDcHeartbeatSender = system.actorSelection(crossDcHeartbeatSenderPath)
 
-      val expectedAlphaHeartbeaterNodes = takeNOldestMembers(_.dataCenter == "alpha", 2)
+      val expectedAlphaHeartbeaterNodes = takeNOldestMembers(dataCenter = "alpha", 2)
       val expectedAlphaHeartbeaterRoles = membersAsRoles(expectedAlphaHeartbeaterNodes)
 
-      val expectedBetaHeartbeaterNodes = takeNOldestMembers(_.dataCenter == "beta", 2)
+      val expectedBetaHeartbeaterNodes = takeNOldestMembers(dataCenter = "beta", 2)
       val expectedBetaHeartbeaterRoles = membersAsRoles(expectedBetaHeartbeaterNodes)
 
       val expectedNoActiveHeartbeatSenderRoles = roles.toSet -- (expectedAlphaHeartbeaterRoles union expectedBetaHeartbeaterRoles)
@@ -147,16 +147,15 @@ abstract class MultiDcSunnyWeatherSpec extends MultiNodeSpec(MultiDcSunnyWeather
    * strongly guaratnee the order of "oldest" members, as they're linearized by the order in which they become Up
    * (since marking that transition is a Leader action).
    */
-  private def membersByAge(): immutable.SortedSet[Member] =
+  private def membersByAge(dataCenter: ClusterSettings.DataCenter): immutable.SortedSet[Member] =
     SortedSet.empty(Member.ageOrdering)
-      .union(cluster.state.members.filter(m ⇒ m.status != MemberStatus.Joining && m.status != MemberStatus.WeaklyUp))
+      .union(cluster.state.members.filter(m ⇒ m.dataCenter == dataCenter &&
+        m.status != MemberStatus.Joining && m.status != MemberStatus.WeaklyUp))
 
   /** INTERNAL API */
   @InternalApi
-  private[cluster] def takeNOldestMembers(memberFilter: Member ⇒ Boolean, n: Int): immutable.SortedSet[Member] =
-    membersByAge()
-      .filter(memberFilter)
-      .take(n)
+  private[cluster] def takeNOldestMembers(dataCenter: ClusterSettings.DataCenter, n: Int): immutable.SortedSet[Member] =
+    membersByAge(dataCenter).take(n)
 
   private def membersAsRoles(ms: immutable.Set[Member]): immutable.Set[RoleName] = {
     val res = ms.flatMap(m ⇒ roleName(m.address))