diff --git a/akka-actor/src/main/scala/akka/serialization/Serializer.scala b/akka-actor/src/main/scala/akka/serialization/Serializer.scala
index 1a4b073cd2..595ca4084b 100644
--- a/akka-actor/src/main/scala/akka/serialization/Serializer.scala
+++ b/akka-actor/src/main/scala/akka/serialization/Serializer.scala
@@ -281,14 +281,6 @@ object JavaSerializer {
  */
 class JavaSerializer(val system: ExtendedActorSystem) extends BaseSerializer {
 
-  @deprecated("Use constructor with ExtendedActorSystem", "2.4")
-  def this() = this(null)
-
-  // TODO remove this when deprecated this() is removed
-  override val identifier: Int =
-    if (system eq null) 1
-    else identifierFromConfig
-
   def includeManifest: Boolean = false
 
   def toBinary(o: AnyRef): Array[Byte] = {
@@ -324,14 +316,6 @@ class NullSerializer extends Serializer {
  */
 class ByteArraySerializer(val system: ExtendedActorSystem) extends BaseSerializer with ByteBufferSerializer {
 
-  @deprecated("Use constructor with ExtendedActorSystem", "2.4")
-  def this() = this(null)
-
-  // TODO remove this when deprecated this() is removed
-  override val identifier: Int =
-    if (system eq null) 4
-    else identifierFromConfig
-
   def includeManifest: Boolean = false
   def toBinary(o: AnyRef): Array[Byte] = o match {
     case null           ⇒ null
diff --git a/akka-cluster/src/main/scala/akka/cluster/protobuf/ClusterMessageSerializer.scala b/akka-cluster/src/main/scala/akka/cluster/protobuf/ClusterMessageSerializer.scala
index dccab336f0..2fcd7f589a 100644
--- a/akka-cluster/src/main/scala/akka/cluster/protobuf/ClusterMessageSerializer.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/protobuf/ClusterMessageSerializer.scala
@@ -26,14 +26,6 @@ import akka.cluster.InternalClusterAction.ExitingConfirmed
  */
 class ClusterMessageSerializer(val system: ExtendedActorSystem) extends BaseSerializer {
 
-  @deprecated("Use constructor with ExtendedActorSystem", "2.4")
-  def this() = this(null)
-
-  // TODO remove this when deprecated this() is removed
-  override val identifier: Int =
-    if (system eq null) 5
-    else identifierFromConfig
-
   private final val BufferSize = 1024 * 4
   // must be lazy because serializer is initialized from Cluster extension constructor
   private lazy val GossipTimeToLive = Cluster(system).settings.GossipTimeToLive
diff --git a/akka-remote/src/main/scala/akka/remote/serialization/MessageContainerSerializer.scala b/akka-remote/src/main/scala/akka/remote/serialization/MessageContainerSerializer.scala
index 1d0e01c3b1..f21906cdc5 100644
--- a/akka-remote/src/main/scala/akka/remote/serialization/MessageContainerSerializer.scala
+++ b/akka-remote/src/main/scala/akka/remote/serialization/MessageContainerSerializer.scala
@@ -18,16 +18,8 @@ import akka.serialization.SerializerWithStringManifest
 
 class MessageContainerSerializer(val system: ExtendedActorSystem) extends BaseSerializer {
 
-  @deprecated("Use constructor with ExtendedActorSystem", "2.4")
-  def this() = this(null)
-
   private lazy val serialization = SerializationExtension(system)
 
-  // TODO remove this when deprecated this() is removed
-  override val identifier: Int =
-    if (system eq null) 6
-    else identifierFromConfig
-
   def includeManifest: Boolean = false
 
   def toBinary(obj: AnyRef): Array[Byte] = obj match {
diff --git a/akka-remote/src/main/scala/akka/remote/serialization/ProtobufSerializer.scala b/akka-remote/src/main/scala/akka/remote/serialization/ProtobufSerializer.scala
index 63e542e3f0..01e7ee8fa0 100644
--- a/akka-remote/src/main/scala/akka/remote/serialization/ProtobufSerializer.scala
+++ b/akka-remote/src/main/scala/akka/remote/serialization/ProtobufSerializer.scala
@@ -40,14 +40,6 @@ object ProtobufSerializer {
  */
 class ProtobufSerializer(val system: ExtendedActorSystem) extends BaseSerializer {
 
-  @deprecated("Use constructor with ExtendedActorSystem", "2.4")
-  def this() = this(null)
-
-  // TODO remove this when deprecated this() is removed
-  override val identifier: Int =
-    if (system eq null) 2
-    else identifierFromConfig
-
   @deprecated("Will be removed without replacement", "2.4")
   val ARRAY_OF_BYTE_ARRAY = Array[Class[_]](classOf[Array[Byte]])
 
diff --git a/project/MiMa.scala b/project/MiMa.scala
index c76edcf4cd..a95c5df839 100644
--- a/project/MiMa.scala
+++ b/project/MiMa.scala
@@ -261,6 +261,14 @@ object MiMa extends AutoPlugin {
       ProblemFilters.exclude[MissingClassProblem]("akka.util.Crypt"),
       ProblemFilters.exclude[MissingClassProblem]("akka.util.Crypt$"),
       
+      // #21423 removal of deprecated serializer constructors (in 2.5.x)
+      ProblemFilters.exclude[DirectMissingMethodProblem]("akka.remote.serialization.ProtobufSerializer.this"),
+      ProblemFilters.exclude[DirectMissingMethodProblem]("akka.remote.serialization.MessageContainerSerializer.this"),
+      ProblemFilters.exclude[DirectMissingMethodProblem]("akka.remote.serialization.DaemonMsgCreateSerializer.this"),
+      ProblemFilters.exclude[DirectMissingMethodProblem]("akka.serialization.JavaSerializer.this"),
+      ProblemFilters.exclude[DirectMissingMethodProblem]("akka.serialization.ByteArraySerializer.this"),
+      ProblemFilters.exclude[DirectMissingMethodProblem]("akka.cluster.protobuf.ClusterMessageSerializer.this"),
+      
       // #21423 removal of deprecated `PersistentView` (in 2.5.x)
       ProblemFilters.exclude[MissingClassProblem]("akka.persistence.Update"),
       ProblemFilters.exclude[MissingClassProblem]("akka.persistence.Update$"),