diff --git a/akka-http/src/main/scala/akka/http/scaladsl/server/Directive.scala b/akka-http/src/main/scala/akka/http/scaladsl/server/Directive.scala
index 87e86c1e04..1acd651801 100644
--- a/akka-http/src/main/scala/akka/http/scaladsl/server/Directive.scala
+++ b/akka-http/src/main/scala/akka/http/scaladsl/server/Directive.scala
@@ -23,7 +23,7 @@ abstract class Directive[L](implicit val ev: Tuple[L]) {
    * which is added by an implicit conversion (see `Directive.addDirectiveApply`).
    */
   def tapply(f: L ⇒ Route): Route
-//#
+  //#
   /**
    * Joins two directives into one which runs the second directive if the first one rejects.
    */
@@ -90,7 +90,7 @@ abstract class Directive[L](implicit val ev: Tuple[L]) {
   def recoverPF[R >: L: Tuple](recovery: PartialFunction[immutable.Seq[Rejection], Directive[R]]): Directive[R] =
     recover { rejections ⇒ recovery.applyOrElse(rejections, (rejs: Seq[Rejection]) ⇒ RouteDirectives.reject(rejs: _*)) }
 
-//#basic
+  //#basic
 }
 //#
 
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala
index e87e093818..c3a420bdb9 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala
@@ -87,7 +87,7 @@ private[stream] object GraphInterpreter {
    * corresponding segments of these arrays matches the exact same order of the ports in the [[Shape]].
    *
    */
-  final class GraphAssembly(val stages: Array[GraphStageWithMaterializedValue[_, _]],
+  final class GraphAssembly(val stages: Array[GraphStageWithMaterializedValue[Shape, Any]],
                             val ins: Array[Inlet[_]],
                             val inOwners: Array[Int],
                             val outs: Array[Outlet[_]],
@@ -113,7 +113,7 @@ private[stream] object GraphInterpreter {
       var i = 0
       while (i < stages.length) {
         // Port initialization loops, these must come first
-        val shape = stages(i).asInstanceOf[GraphStageWithMaterializedValue[Shape, _]].shape
+        val shape = stages(i).shape
 
         var idx = 0
         val inletItr = shape.inlets.iterator
@@ -185,7 +185,7 @@ private[stream] object GraphInterpreter {
      */
     final def apply(inlets: immutable.Seq[Inlet[_]],
                     outlets: immutable.Seq[Outlet[_]],
-                    stages: GraphStageWithMaterializedValue[_, _]*): GraphAssembly = {
+                    stages: GraphStageWithMaterializedValue[Shape, _]*): GraphAssembly = {
       // add the contents of an iterator to an array starting at idx
       @tailrec def add[T](i: Iterator[T], a: Array[T], idx: Int): Array[T] =
         if (i.hasNext) {
@@ -317,7 +317,7 @@ private[stream] final class GraphInterpreter(
 
   // Counts how many active connections a stage has. Once it reaches zero, the stage is automatically stopped.
   private[this] val shutdownCounter = Array.tabulate(assembly.stages.length) { i ⇒
-    val shape = assembly.stages(i).shape.asInstanceOf[Shape]
+    val shape = assembly.stages(i).shape
     shape.inlets.size + shape.outlets.size
   }
 
diff --git a/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala b/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala
index fdc3bc5e7c..0da78ee2bf 100644
--- a/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala
+++ b/akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala
@@ -12,13 +12,12 @@ import scala.collection.{ immutable, mutable }
 import scala.concurrent.duration.FiniteDuration
 import scala.collection.mutable.ArrayBuffer
 
-abstract class GraphStageWithMaterializedValue[S <: Shape, M] extends Graph[S, M] {
-  def shape: S
+abstract class GraphStageWithMaterializedValue[+S <: Shape, +M] extends Graph[S, M] {
   def createLogicAndMaterializedValue: (GraphStageLogic, M)
 
   final override private[stream] lazy val module: Module =
     GraphModule(
-      GraphAssembly(shape.inlets, shape.outlets, Array(this): _*),
+      GraphAssembly(shape.inlets, shape.outlets, this),
       shape,
       Attributes.none)