diff --git a/akka-actor-tests/src/test/scala/akka/util/IndexSpec.scala b/akka-actor-tests/src/test/scala/akka/util/IndexSpec.scala
index 8c14979a09..7eb88f927c 100644
--- a/akka-actor-tests/src/test/scala/akka/util/IndexSpec.scala
+++ b/akka-actor-tests/src/test/scala/akka/util/IndexSpec.scala
@@ -3,6 +3,7 @@
  */
 package akka.util
 
+import java.util.Comparator
 import org.scalatest.Matchers
 import scala.concurrent.Future
 import akka.testkit.AkkaSpec
@@ -12,7 +13,9 @@ import akka.testkit.DefaultTimeout
 
 class IndexSpec extends AkkaSpec with Matchers with DefaultTimeout {
   implicit val ec = system.dispatcher
-  private def emptyIndex = new Index[String, Int](100, _ compareTo _)
+  private def emptyIndex = new Index[String, Int](100, new Comparator[Int] {
+    override def compare(a: Int, b: Int): Int = Integer.compare(a, b)
+  })
 
   private def indexWithValues = {
     val index = emptyIndex
@@ -92,7 +95,9 @@ class IndexSpec extends AkkaSpec with Matchers with DefaultTimeout {
       index.isEmpty should ===(true)
     }
     "be able to be accessed in parallel" in {
-      val index = new Index[Int, Int](100, _ compareTo _)
+      val index = new Index[Int, Int](100, new Comparator[Int] {
+        override def compare(a: Int, b: Int): Int = Integer.compare(a, b)
+      })
       val nrOfTasks = 10000
       val nrOfKeys = 10
       val nrOfValues = 10
diff --git a/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala b/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala
index 52ada0fc04..b0fb0a2625 100644
--- a/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala
@@ -59,7 +59,9 @@ private[akka] object MessageDispatcher {
   // dispatcher debugging helper using println (see below)
   // since this is a compile-time constant, scalac will elide code behind if (MessageDispatcher.debug) (RK checked with 2.9.1)
   final val debug = false // Deliberately without type ascription to make it a compile-time constant
-  lazy val actors = new Index[MessageDispatcher, ActorRef](16, _ compareTo _)
+  lazy val actors = new Index[MessageDispatcher, ActorRef](16, new ju.Comparator[ActorRef] {
+    override def compare(a: ActorRef, b: ActorRef): Int = a.compareTo(b)
+  })
   def printActors(): Unit =
     if (debug) {
       for {
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 365c90ae24..27fcc7717d 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -12,18 +12,29 @@ object Dependencies {
   lazy val scalaTestVersion = settingKey[String]("The version of ScalaTest to use.")
   lazy val scalaStmVersion = settingKey[String]("The version of ScalaSTM to use.")
   lazy val scalaCheckVersion = settingKey[String]("The version of ScalaCheck to use.")
+  lazy val java8CompatVersion = settingKey[String]("The version of scala-java8-compat to use.")
   val junitVersion = "4.12"
 
   val Versions = Seq(
-    crossScalaVersions := Seq("2.11.7"), // "2.12.0-M3"
+    crossScalaVersions := Seq("2.11.7"), // "2.12.0-M4"
     scalaVersion := crossScalaVersions.value.head,
     scalaStmVersion := sys.props.get("akka.build.scalaStmVersion").getOrElse("0.7"),
     scalaCheckVersion := sys.props.get("akka.build.scalaCheckVersion").getOrElse("1.11.6"),
-    scalaTestVersion := (
-      if (scalaVersion.value == "2.12.0-M2") "2.2.5-M2"
-      else if (scalaVersion.value == "2.12.0-M3") "2.2.5-M3"
-      else "2.2.4"
-    )
+    scalaTestVersion := {
+      scalaVersion.value match {
+        case "2.12.0-M1" => "2.2.5-M1"
+        case "2.12.0-M2" => "2.2.5-M2"
+        case "2.12.0-M3" => "2.2.5-M3"
+        case "2.12.0-M4" => "2.2.6"
+        case _ => "2.2.4"
+      }
+    },
+    java8CompatVersion := {
+      scalaVersion.value match {
+        case "2.12.0-M4" => "0.8.0-RC1"
+        case _ => "0.7.0"
+      }
+    }
   )
 
   object Compile {
@@ -65,7 +76,7 @@ object Dependencies {
     val junit       = "junit"                         % "junit"                        % junitVersion  // Common Public License 1.0
 
     // For Java 8 Conversions
-    val java8Compat = "org.scala-lang.modules"       %% "scala-java8-compat"           % "0.7.0"       // Scala License
+    val java8Compat = Def.setting {"org.scala-lang.modules" %% "scala-java8-compat" % java8CompatVersion.value} // Scala License
 
     object Docs {
       val sprayJson   = "io.spray"                   %%  "spray-json"                  % "1.3.2"             % "test"
@@ -119,7 +130,7 @@ object Dependencies {
   // TODO check if `l ++=` everywhere expensive?
   val l = libraryDependencies
 
-  val actor = l ++= Seq(config, java8Compat)
+  val actor = l ++= Seq(config, java8Compat.value)
 
   val testkit = l ++= Seq(Test.junit, Test.scalatest.value) ++ Test.metricsAll
 
@@ -166,11 +177,10 @@ object Dependencies {
   // akka stream & http
 
   lazy val httpCore = l ++= Seq(
-    java8Compat,
     Test.sprayJson, // for WS Autobahn test metadata
     Test.junitIntf, Test.junit, Test.scalatest.value)
 
-  lazy val http = l ++= Seq(java8Compat)
+  lazy val http = l ++= Nil
 
   // special, since it also includes a compiler plugin
   lazy val parsing = Seq(