diff --git a/akka-actor-tests/src/test/java/akka/actor/JavaExtension.java b/akka-actor-tests/src/test/java/akka/actor/JavaExtension.java
index 812e79e2874..28b87bb5dbb 100644
--- a/akka-actor-tests/src/test/java/akka/actor/JavaExtension.java
+++ b/akka-actor-tests/src/test/java/akka/actor/JavaExtension.java
@@ -23,15 +23,15 @@ public ExtensionId<TestExtension> lookup() {
       return TestExtensionId.TestExtensionProvider;
     }
 
-    public TestExtension createExtension(ActorSystemImpl i) {
+    public TestExtension createExtension(ExtendedActorSystem i) {
       return new TestExtension(i);
     }
   }
 
   static class TestExtension implements Extension {
-    public final ActorSystemImpl system;
+    public final ExtendedActorSystem system;
 
-    public TestExtension(ActorSystemImpl i) {
+    public TestExtension(ExtendedActorSystem i) {
       system = i;
     }
   }
diff --git a/akka-actor-tests/src/test/scala/akka/actor/ActorSystemSpec.scala b/akka-actor-tests/src/test/scala/akka/actor/ActorSystemSpec.scala
index 9391ad43d1c..ea8ce4c7d04 100644
--- a/akka-actor-tests/src/test/scala/akka/actor/ActorSystemSpec.scala
+++ b/akka-actor-tests/src/test/scala/akka/actor/ActorSystemSpec.scala
@@ -15,11 +15,11 @@ class JavaExtensionSpec extends JavaExtension with JUnitSuite
 
 object TestExtension extends ExtensionId[TestExtension] with ExtensionIdProvider {
   def lookup = this
-  def createExtension(s: ActorSystemImpl) = new TestExtension(s)
+  def createExtension(s: ExtendedActorSystem) = new TestExtension(s)
 }
 
 // Dont't place inside ActorSystemSpec object, since it will not be garbage collected and reference to system remains
-class TestExtension(val system: ActorSystemImpl) extends Extension
+class TestExtension(val system: ExtendedActorSystem) extends Extension
 
 @org.junit.runner.RunWith(classOf[org.scalatest.junit.JUnitRunner])
 class ActorSystemSpec extends AkkaSpec("""akka.extensions = ["akka.actor.TestExtension$"]""") {
diff --git a/akka-actor-tests/src/test/scala/akka/performance/trading/domain/TradeObserver.scala b/akka-actor-tests/src/test/scala/akka/performance/trading/domain/TradeObserver.scala
index be867121f55..870a2df79d5 100644
--- a/akka-actor-tests/src/test/scala/akka/performance/trading/domain/TradeObserver.scala
+++ b/akka-actor-tests/src/test/scala/akka/performance/trading/domain/TradeObserver.scala
@@ -1,11 +1,8 @@
 package akka.performance.trading.domain
 
 import java.util.concurrent.atomic.AtomicInteger
-import akka.actor.Extension
-import akka.actor.ExtensionId
-import akka.actor.ExtensionIdProvider
-import akka.actor.ActorSystemImpl
-import akka.actor.ActorSystem
+
+import akka.actor.{ ExtensionIdProvider, ExtensionId, Extension, ExtendedActorSystem, ActorSystem }
 
 abstract trait TradeObserver {
   def trade(bid: Bid, ask: Ask)
@@ -38,5 +35,5 @@ object TotalTradeCounterExtension
   extends ExtensionId[TotalTradeCounter]
   with ExtensionIdProvider {
   override def lookup = TotalTradeCounterExtension
-  override def createExtension(system: ActorSystemImpl) = new TotalTradeCounter
+  override def createExtension(system: ExtendedActorSystem) = new TotalTradeCounter
 }
\ No newline at end of file
diff --git a/akka-actor/src/main/scala/akka/actor/ActorSystem.scala b/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
index b77aac491f1..c6842d0dc2f 100644
--- a/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
+++ b/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
@@ -130,6 +130,13 @@ object ActorSystem {
  * }}}
  *
  * Where no name is given explicitly, one will be automatically generated.
+ *
+ * <b><i>Important Notice:</i></o>
+ *
+ * This class is not meant to be extended by user code. If you want to
+ * actually roll your own Akka, it will probably be better to look into
+ * extending [[akka.actor.ExtendedActorSystem]] instead, but beware that you
+ * are completely on your own in that case!
  */
 abstract class ActorSystem extends ActorRefFactory {
   import ActorSystem._
@@ -286,7 +293,40 @@ abstract class ActorSystem extends ActorRefFactory {
   def hasExtension(ext: ExtensionId[_ <: Extension]): Boolean
 }
 
-class ActorSystemImpl(val name: String, applicationConfig: Config) extends ActorSystem {
+/**
+ * More powerful interface to the actor system’s implementation which is presented to extensions (see [[akka.actor.Extension]]).
+ *
+ * <b><i>Important Notice:</i></o>
+ *
+ * This class is not meant to be extended by user code. If you want to
+ * actually roll your own Akka, beware that you are completely on your own in
+ * that case!
+ */
+abstract class ExtendedActorSystem extends ActorSystem {
+
+  /**
+   * The ActorRefProvider is the only entity which creates all actor references within this actor system.
+   */
+  def provider: ActorRefProvider
+
+  /**
+   * The top-level supervisor of all actors created using system.actorOf(...).
+   */
+  def guardian: InternalActorRef
+
+  /**
+   * The top-level supervisor of all system-internal services like logging.
+   */
+  def systemGuardian: InternalActorRef
+
+  /**
+   * Implementation of the mechanism which is used for watch()/unwatch().
+   */
+  def deathWatch: DeathWatch
+
+}
+
+class ActorSystemImpl(val name: String, applicationConfig: Config) extends ExtendedActorSystem {
 
   if (!name.matches("""^\w+$"""))
     throw new IllegalArgumentException("invalid ActorSystem name [" + name + "], must contain only word characters (i.e. [a-zA-Z_0-9])")
diff --git a/akka-actor/src/main/scala/akka/actor/Extension.scala b/akka-actor/src/main/scala/akka/actor/Extension.scala
index 18506614170..f60d6afb222 100644
--- a/akka-actor/src/main/scala/akka/actor/Extension.scala
+++ b/akka-actor/src/main/scala/akka/actor/Extension.scala
@@ -18,10 +18,8 @@ import akka.util.ReflectiveAccess
  * The extension itself can be created in any way desired and has full access
  * to the ActorSystem implementation.
  *
- */
-
-/**
- * Marker interface to signify an Akka Extension
+ * This trait is only a marker interface to signify an Akka Extension, see
+ * [[akka.actor.ExtensionKey]] for a concise way of formulating extensions.
  */
 trait Extension
 
@@ -47,7 +45,7 @@ trait ExtensionId[T <: Extension] {
    * Is used by Akka to instantiate the Extension identified by this ExtensionId,
    * internal use only.
    */
-  def createExtension(system: ActorSystemImpl): T
+  def createExtension(system: ExtendedActorSystem): T
 }
 
 /**
@@ -94,7 +92,7 @@ abstract class ExtensionKey[T <: Extension](implicit m: ClassManifest[T]) extend
   def this(clazz: Class[T]) = this()(ClassManifest.fromClass(clazz))
 
   override def lookup(): ExtensionId[T] = this
-  def createExtension(system: ActorSystemImpl): T =
+  def createExtension(system: ExtendedActorSystem): T =
     ReflectiveAccess.createInstance[T](m.erasure, Array[Class[_]](classOf[ActorSystemImpl]), Array[AnyRef](system)) match {
       case Left(ex) ⇒ throw ex
       case Right(r) ⇒ r
diff --git a/akka-actor/src/main/scala/akka/actor/IO.scala b/akka-actor/src/main/scala/akka/actor/IO.scala
index b7942975d9d..1ee38da4b97 100644
--- a/akka-actor/src/main/scala/akka/actor/IO.scala
+++ b/akka-actor/src/main/scala/akka/actor/IO.scala
@@ -744,7 +744,7 @@ final class IOManager private (system: ActorSystem) extends Extension {
 
 object IOManager extends ExtensionId[IOManager] with ExtensionIdProvider {
   override def lookup = this
-  override def createExtension(system: ActorSystemImpl) = new IOManager(system)
+  override def createExtension(system: ExtendedActorSystem) = new IOManager(system)
 }
 
 /**
diff --git a/akka-actor/src/main/scala/akka/actor/TypedActor.scala b/akka-actor/src/main/scala/akka/actor/TypedActor.scala
index 3293add1517..ce487ec2ef0 100644
--- a/akka-actor/src/main/scala/akka/actor/TypedActor.scala
+++ b/akka-actor/src/main/scala/akka/actor/TypedActor.scala
@@ -80,7 +80,7 @@ object TypedActor extends ExtensionId[TypedActorExtension] with ExtensionIdProvi
   override def get(system: ActorSystem): TypedActorExtension = super.get(system)
 
   def lookup() = this
-  def createExtension(system: ActorSystemImpl): TypedActorExtension = new TypedActorExtension(system)
+  def createExtension(system: ExtendedActorSystem): TypedActorExtension = new TypedActorExtension(system)
 
   /**
    * Returns a contextual TypedActorFactory of this extension, this means that any TypedActors created by this TypedActorExtension
@@ -531,7 +531,7 @@ case class ContextualTypedActorFactory(typedActor: TypedActorExtension, actorFac
   override def isTypedActor(proxyOrNot: AnyRef): Boolean = typedActor.isTypedActor(proxyOrNot)
 }
 
-class TypedActorExtension(system: ActorSystemImpl) extends TypedActorFactory with Extension {
+class TypedActorExtension(system: ExtendedActorSystem) extends TypedActorFactory with Extension {
   import TypedActor._ //Import the goodies from the companion object
   protected def actorFactory: ActorRefFactory = system
   protected def typedActor = this
diff --git a/akka-actor/src/main/scala/akka/serialization/Serialization.scala b/akka-actor/src/main/scala/akka/serialization/Serialization.scala
index eaa0ce09250..78cb370b685 100644
--- a/akka-actor/src/main/scala/akka/serialization/Serialization.scala
+++ b/akka-actor/src/main/scala/akka/serialization/Serialization.scala
@@ -9,7 +9,7 @@ import akka.util.ReflectiveAccess
 import scala.util.DynamicVariable
 import com.typesafe.config.Config
 import akka.config.ConfigurationException
-import akka.actor.{ Extension, ActorSystem, ActorSystemImpl }
+import akka.actor.{ Extension, ActorSystem, ExtendedActorSystem }
 
 case class NoSerializerFoundException(m: String) extends AkkaException(m)
 
@@ -55,7 +55,7 @@ object Serialization {
  * Serialization module. Contains methods for serialization and deserialization as well as
  * locating a Serializer for a particular class as defined in the mapping in the 'akka.conf' file.
  */
-class Serialization(val system: ActorSystemImpl) extends Extension {
+class Serialization(val system: ExtendedActorSystem) extends Extension {
   import Serialization._
 
   val settings = new Settings(system.settings.config)
diff --git a/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala b/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala
index 9d9815f412e..f96aa26e0ce 100644
--- a/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala
+++ b/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala
@@ -3,7 +3,7 @@
  */
 package akka.serialization
 
-import akka.actor.{ ActorSystem, ExtensionId, ExtensionIdProvider, ActorSystemImpl }
+import akka.actor.{ ActorSystem, ExtensionId, ExtensionIdProvider, ExtendedActorSystem }
 
 /**
  * SerializationExtension is an Akka Extension to interact with the Serialization
@@ -12,5 +12,5 @@ import akka.actor.{ ActorSystem, ExtensionId, ExtensionIdProvider, ActorSystemIm
 object SerializationExtension extends ExtensionId[Serialization] with ExtensionIdProvider {
   override def get(system: ActorSystem): Serialization = super.get(system)
   override def lookup = SerializationExtension
-  override def createExtension(system: ActorSystemImpl): Serialization = new Serialization(system)
+  override def createExtension(system: ExtendedActorSystem): Serialization = new Serialization(system)
 }
\ No newline at end of file
diff --git a/akka-docs/java/code/akka/docs/extension/ExtensionDocTestBase.java b/akka-docs/java/code/akka/docs/extension/ExtensionDocTestBase.java
index 6d62eb5bb89..11dfe4c198b 100644
--- a/akka-docs/java/code/akka/docs/extension/ExtensionDocTestBase.java
+++ b/akka-docs/java/code/akka/docs/extension/ExtensionDocTestBase.java
@@ -42,7 +42,7 @@ public CountExtension lookup() {
 
     //This method will be called by Akka
     // to instantiate our Extension
-    public CountExtensionImpl createExtension(ActorSystemImpl system) {
+    public CountExtensionImpl createExtension(ExtendedActorSystem system) {
       return new CountExtensionImpl();
     }
   }
diff --git a/akka-docs/java/code/akka/docs/extension/SettingsExtensionDocTestBase.java b/akka-docs/java/code/akka/docs/extension/SettingsExtensionDocTestBase.java
index 6ca1c371d9b..1bf6ce7c36e 100644
--- a/akka-docs/java/code/akka/docs/extension/SettingsExtensionDocTestBase.java
+++ b/akka-docs/java/code/akka/docs/extension/SettingsExtensionDocTestBase.java
@@ -8,7 +8,7 @@
 import akka.actor.AbstractExtensionId;
 import akka.actor.ExtensionIdProvider;
 import akka.actor.ActorSystem;
-import akka.actor.ActorSystemImpl;
+import akka.actor.ExtendedActorSystem;
 import akka.util.Duration;
 import com.typesafe.config.Config;
 import java.util.concurrent.TimeUnit;
@@ -44,7 +44,7 @@ public Settings lookup() {
       return Settings.SettingsProvider;
     }
 
-    public SettingsImpl createExtension(ActorSystemImpl system) {
+    public SettingsImpl createExtension(ExtendedActorSystem system) {
       return new SettingsImpl(system.settings().config());
     }
   }
diff --git a/akka-docs/scala/code/akka/docs/extension/ExtensionDocSpec.scala b/akka-docs/scala/code/akka/docs/extension/ExtensionDocSpec.scala
index 1f4d777ad9a..0c778a48122 100644
--- a/akka-docs/scala/code/akka/docs/extension/ExtensionDocSpec.scala
+++ b/akka-docs/scala/code/akka/docs/extension/ExtensionDocSpec.scala
@@ -23,7 +23,7 @@ class CountExtensionImpl extends Extension {
 //#extensionid
 import akka.actor.ExtensionId
 import akka.actor.ExtensionIdProvider
-import akka.actor.ActorSystemImpl
+import akka.actor.ExtendedActorSystem
 
 object CountExtension
   extends ExtensionId[CountExtensionImpl]
@@ -36,7 +36,7 @@ object CountExtension
 
   //This method will be called by Akka
   // to instantiate our Extension
-  override def createExtension(system: ActorSystemImpl) = new CountExtensionImpl
+  override def createExtension(system: ExtendedActorSystem) = new CountExtensionImpl
 }
 //#extensionid
 
diff --git a/akka-docs/scala/code/akka/docs/extension/SettingsExtensionDocSpec.scala b/akka-docs/scala/code/akka/docs/extension/SettingsExtensionDocSpec.scala
index ed5ec66517b..05765d27a57 100644
--- a/akka-docs/scala/code/akka/docs/extension/SettingsExtensionDocSpec.scala
+++ b/akka-docs/scala/code/akka/docs/extension/SettingsExtensionDocSpec.scala
@@ -7,7 +7,7 @@ package akka.docs.extension
 import akka.actor.Extension
 import akka.actor.ExtensionId
 import akka.actor.ExtensionIdProvider
-import akka.actor.ActorSystemImpl
+import akka.actor.ExtendedActorSystem
 import akka.util.Duration
 import com.typesafe.config.Config
 import java.util.concurrent.TimeUnit
@@ -29,7 +29,7 @@ object Settings extends ExtensionId[SettingsImpl] with ExtensionIdProvider {
 
   override def lookup = Settings
 
-  override def createExtension(system: ActorSystemImpl) = new SettingsImpl(system.settings.config)
+  override def createExtension(system: ExtendedActorSystem) = new SettingsImpl(system.settings.config)
 }
 //#extensionid
 
diff --git a/akka-durable-mailboxes/akka-beanstalk-mailbox/src/main/scala/akka/actor/mailbox/BeanstalkBasedMailboxExtension.scala b/akka-durable-mailboxes/akka-beanstalk-mailbox/src/main/scala/akka/actor/mailbox/BeanstalkBasedMailboxExtension.scala
index 91e8085778f..36ab10393ac 100644
--- a/akka-durable-mailboxes/akka-beanstalk-mailbox/src/main/scala/akka/actor/mailbox/BeanstalkBasedMailboxExtension.scala
+++ b/akka-durable-mailboxes/akka-beanstalk-mailbox/src/main/scala/akka/actor/mailbox/BeanstalkBasedMailboxExtension.scala
@@ -11,7 +11,7 @@ import akka.actor._
 object BeanstalkBasedMailboxExtension extends ExtensionId[BeanstalkMailboxSettings] with ExtensionIdProvider {
   override def get(system: ActorSystem): BeanstalkMailboxSettings = super.get(system)
   def lookup() = this
-  def createExtension(system: ActorSystemImpl) = new BeanstalkMailboxSettings(system.settings.config)
+  def createExtension(system: ExtendedActorSystem) = new BeanstalkMailboxSettings(system.settings.config)
 }
 
 class BeanstalkMailboxSettings(val config: Config) extends Extension {
diff --git a/akka-durable-mailboxes/akka-file-mailbox/src/main/scala/akka/actor/mailbox/FileBasedMailboxExtension.scala b/akka-durable-mailboxes/akka-file-mailbox/src/main/scala/akka/actor/mailbox/FileBasedMailboxExtension.scala
index c09bfc9cb36..f7e6527499e 100644
--- a/akka-durable-mailboxes/akka-file-mailbox/src/main/scala/akka/actor/mailbox/FileBasedMailboxExtension.scala
+++ b/akka-durable-mailboxes/akka-file-mailbox/src/main/scala/akka/actor/mailbox/FileBasedMailboxExtension.scala
@@ -11,7 +11,7 @@ import akka.actor._
 object FileBasedMailboxExtension extends ExtensionId[FileBasedMailboxSettings] with ExtensionIdProvider {
   override def get(system: ActorSystem): FileBasedMailboxSettings = super.get(system)
   def lookup() = this
-  def createExtension(system: ActorSystemImpl) = new FileBasedMailboxSettings(system.settings.config)
+  def createExtension(system: ExtendedActorSystem) = new FileBasedMailboxSettings(system.settings.config)
 }
 
 class FileBasedMailboxSettings(val config: Config) extends Extension {
diff --git a/akka-durable-mailboxes/akka-mongo-mailbox/src/main/scala/akka/actor/mailbox/MongoBasedMailboxExtension.scala b/akka-durable-mailboxes/akka-mongo-mailbox/src/main/scala/akka/actor/mailbox/MongoBasedMailboxExtension.scala
index 0176fc09f35..fac0ad9050a 100644
--- a/akka-durable-mailboxes/akka-mongo-mailbox/src/main/scala/akka/actor/mailbox/MongoBasedMailboxExtension.scala
+++ b/akka-durable-mailboxes/akka-mongo-mailbox/src/main/scala/akka/actor/mailbox/MongoBasedMailboxExtension.scala
@@ -11,7 +11,7 @@ import akka.actor._
 object MongoBasedMailboxExtension extends ExtensionId[MongoBasedMailboxSettings] with ExtensionIdProvider {
   override def get(system: ActorSystem): MongoBasedMailboxSettings = super.get(system)
   def lookup() = this
-  def createExtension(system: ActorSystemImpl) = new MongoBasedMailboxSettings(system.settings.config)
+  def createExtension(system: ExtendedActorSystem) = new MongoBasedMailboxSettings(system.settings.config)
 }
 
 class MongoBasedMailboxSettings(val config: Config) extends Extension {
diff --git a/akka-durable-mailboxes/akka-redis-mailbox/src/main/scala/akka/actor/mailbox/RedisBasedMailboxExtension.scala b/akka-durable-mailboxes/akka-redis-mailbox/src/main/scala/akka/actor/mailbox/RedisBasedMailboxExtension.scala
index 17ce4792447..629f08b1457 100644
--- a/akka-durable-mailboxes/akka-redis-mailbox/src/main/scala/akka/actor/mailbox/RedisBasedMailboxExtension.scala
+++ b/akka-durable-mailboxes/akka-redis-mailbox/src/main/scala/akka/actor/mailbox/RedisBasedMailboxExtension.scala
@@ -9,7 +9,7 @@ import akka.actor._
 object RedisBasedMailboxExtension extends ExtensionId[RedisBasedMailboxSettings] with ExtensionIdProvider {
   override def get(system: ActorSystem): RedisBasedMailboxSettings = super.get(system)
   def lookup() = this
-  def createExtension(system: ActorSystemImpl) = new RedisBasedMailboxSettings(system.settings.config)
+  def createExtension(system: ExtendedActorSystem) = new RedisBasedMailboxSettings(system.settings.config)
 }
 
 class RedisBasedMailboxSettings(val config: Config) extends Extension {
diff --git a/akka-durable-mailboxes/akka-zookeeper-mailbox/src/main/scala/akka/actor/mailbox/ZooKeeperBasedMailboxExtension.scala b/akka-durable-mailboxes/akka-zookeeper-mailbox/src/main/scala/akka/actor/mailbox/ZooKeeperBasedMailboxExtension.scala
index de2f2d586f9..4f3dcfb42f5 100644
--- a/akka-durable-mailboxes/akka-zookeeper-mailbox/src/main/scala/akka/actor/mailbox/ZooKeeperBasedMailboxExtension.scala
+++ b/akka-durable-mailboxes/akka-zookeeper-mailbox/src/main/scala/akka/actor/mailbox/ZooKeeperBasedMailboxExtension.scala
@@ -11,7 +11,7 @@ import akka.actor._
 object ZooKeeperBasedMailboxExtension extends ExtensionId[ZooKeeperBasedMailboxSettings] with ExtensionIdProvider {
   override def get(system: ActorSystem): ZooKeeperBasedMailboxSettings = super.get(system)
   def lookup() = this
-  def createExtension(system: ActorSystemImpl) = new ZooKeeperBasedMailboxSettings(system.settings.config)
+  def createExtension(system: ExtendedActorSystem) = new ZooKeeperBasedMailboxSettings(system.settings.config)
 }
 class ZooKeeperBasedMailboxSettings(val config: Config) extends Extension {
 
diff --git a/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala b/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala
index a3a1982e9fd..96d9f8241a7 100644
--- a/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala
@@ -3,26 +3,20 @@
  */
 package akka.testkit
 
-import akka.event.Logging.{ Warning, Error }
+import java.lang.ref.WeakReference
 import java.util.concurrent.locks.ReentrantLock
 import java.util.LinkedList
-import java.util.concurrent.RejectedExecutionException
-import akka.util.Switch
-import java.lang.ref.WeakReference
+
 import scala.annotation.tailrec
-import akka.actor.{ ActorCell, ActorRef, ActorSystem }
-import akka.dispatch._
-import akka.actor.Scheduler
-import akka.event.EventStream
-import akka.util.Duration
-import akka.util.duration._
-import java.util.concurrent.TimeUnit
-import akka.actor.ExtensionId
-import akka.actor.ExtensionIdProvider
-import akka.actor.ActorSystemImpl
-import akka.actor.Extension
+
 import com.typesafe.config.Config
 
+import CallingThreadDispatcher.Id
+import akka.actor.{ ExtensionIdProvider, ExtensionId, Extension, ExtendedActorSystem, ActorRef, ActorCell }
+import akka.dispatch.{ TaskInvocation, SystemMessage, Suspend, Resume, MessageDispatcherConfigurator, MessageDispatcher, Mailbox, Envelope, DispatcherPrerequisites, DefaultSystemMessageQueue }
+import akka.util.duration.intToDurationInt
+import akka.util.{ Switch, Duration }
+
 /*
  * Locking rules:
  *
@@ -42,7 +36,7 @@ import com.typesafe.config.Config
 
 private[testkit] object CallingThreadDispatcherQueues extends ExtensionId[CallingThreadDispatcherQueues] with ExtensionIdProvider {
   override def lookup = CallingThreadDispatcherQueues
-  override def createExtension(system: ActorSystemImpl): CallingThreadDispatcherQueues = new CallingThreadDispatcherQueues
+  override def createExtension(system: ExtendedActorSystem): CallingThreadDispatcherQueues = new CallingThreadDispatcherQueues
 }
 
 private[testkit] class CallingThreadDispatcherQueues extends Extension {
diff --git a/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala b/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala
index 89c40f48f48..ada5a4fd302 100644
--- a/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala
@@ -6,11 +6,11 @@ package akka.testkit
 import com.typesafe.config.Config
 import akka.util.Duration
 import java.util.concurrent.TimeUnit.MILLISECONDS
-import akka.actor.{ ExtensionId, ActorSystem, Extension, ActorSystemImpl }
+import akka.actor.{ ExtensionId, ActorSystem, Extension, ExtendedActorSystem }
 
 object TestKitExtension extends ExtensionId[TestKitSettings] {
   override def get(system: ActorSystem): TestKitSettings = super.get(system)
-  def createExtension(system: ActorSystemImpl): TestKitSettings = new TestKitSettings(system.settings.config)
+  def createExtension(system: ExtendedActorSystem): TestKitSettings = new TestKitSettings(system.settings.config)
 }
 
 class TestKitSettings(val config: Config) extends Extension {
diff --git a/akka-zeromq/src/main/scala/akka/zeromq/ZeroMQExtension.scala b/akka-zeromq/src/main/scala/akka/zeromq/ZeroMQExtension.scala
index f0dee326b2c..c0486fa3ab1 100644
--- a/akka-zeromq/src/main/scala/akka/zeromq/ZeroMQExtension.scala
+++ b/akka-zeromq/src/main/scala/akka/zeromq/ZeroMQExtension.scala
@@ -24,7 +24,7 @@ case class ZeroMQVersion(major: Int, minor: Int, patch: Int) {
  */
 object ZeroMQExtension extends ExtensionId[ZeroMQExtension] with ExtensionIdProvider {
   def lookup() = this
-  def createExtension(system: ActorSystemImpl) = new ZeroMQExtension(system)
+  def createExtension(system: ExtendedActorSystem) = new ZeroMQExtension(system)
 
   private val minVersionString = "2.1.0"
   private val minVersion = JZMQ.makeVersion(2, 1, 0)