diff --git a/akka-cluster/src/main/scala/akka/cluster/ClusterEvent.scala b/akka-cluster/src/main/scala/akka/cluster/ClusterEvent.scala
index 72852ad5fe..9632de5213 100644
--- a/akka-cluster/src/main/scala/akka/cluster/ClusterEvent.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/ClusterEvent.scala
@@ -210,7 +210,9 @@ object ClusterEvent {
    * Marker interface to facilitate subscription of
    * both [[UnreachableMember]] and [[ReachableMember]].
    */
-  sealed trait ReachabilityEvent extends ClusterDomainEvent
+  sealed trait ReachabilityEvent extends ClusterDomainEvent {
+    def member: Member
+  }
 
   /**
    * A member is considered as unreachable by the failure detector.
diff --git a/project/MiMa.scala b/project/MiMa.scala
index 8a130880fd..94955a013f 100644
--- a/project/MiMa.scala
+++ b/project/MiMa.scala
@@ -528,7 +528,11 @@ object MiMa extends AutoPlugin {
         ProblemFilters.exclude[MissingClassProblem]("akka.stream.stage.UpstreamDirective"),
         ProblemFilters.exclude[MissingClassProblem]("akka.stream.stage.FreeDirective"),
         ProblemFilters.exclude[MissingClassProblem]("akka.stream.stage.StatefulStage$AndThen"),
-        ProblemFilters.exclude[MissingClassProblem]("akka.stream.stage.SyncDirective")
+        ProblemFilters.exclude[MissingClassProblem]("akka.stream.stage.SyncDirective"),
+
+        // # 21944
+        ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.cluster.ClusterEvent#ReachabilityEvent.member")
+
       )
     )
   }