diff --git a/akka-bench-jmh/src/main/scala/akka/stream/EmptySourceBenchmark.scala b/akka-bench-jmh/src/main/scala/akka/stream/EmptySourceBenchmark.scala
index d149a56ec0..c262f88211 100644
--- a/akka-bench-jmh/src/main/scala/akka/stream/EmptySourceBenchmark.scala
+++ b/akka-bench-jmh/src/main/scala/akka/stream/EmptySourceBenchmark.scala
@@ -22,18 +22,16 @@ class EmptySourceBenchmark {
   val materializerSettings = ActorMaterializerSettings(system).withDispatcher("akka.test.stream-dispatcher")
   implicit val materializer = ActorMaterializer(materializerSettings)
 
-
   @TearDown
   def shutdown(): Unit = {
     Await.result(system.terminate(), 5.seconds)
   }
 
   val setup = Source.empty[String].toMat(Sink.ignore)(Keep.right)
-  
-  @Benchmark def empty(): Unit = 
+
+  @Benchmark def empty(): Unit =
     Await.result(setup.run(), Duration.Inf)
 
-  
   /*
     (not serious benchmark, just sanity check: run on macbook 15, late 2013)
   
diff --git a/akka-bench-jmh/src/main/scala/akka/stream/MaterializationBenchmark.scala b/akka-bench-jmh/src/main/scala/akka/stream/MaterializationBenchmark.scala
index 1c589ed0d1..32e8da50e7 100644
--- a/akka-bench-jmh/src/main/scala/akka/stream/MaterializationBenchmark.scala
+++ b/akka-bench-jmh/src/main/scala/akka/stream/MaterializationBenchmark.scala
@@ -84,7 +84,7 @@ class MaterializationBenchmark {
   var graphWithNestedImports: RunnableGraph[NotUsed] = _
   var graphWithImportedFlow: RunnableGraph[NotUsed] = _
 
-  @Param(Array("1", "10"))
+  @Param(Array("1", "10", "100", "1000"))
   var complexity = 0
 
   @Setup
diff --git a/akka-stream/src/main/scala/akka/stream/impl/PhasedFusingActorMaterializer.scala b/akka-stream/src/main/scala/akka/stream/impl/PhasedFusingActorMaterializer.scala
index 63a260879a..f6b41fce9a 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/PhasedFusingActorMaterializer.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/PhasedFusingActorMaterializer.scala
@@ -581,7 +581,7 @@ final class GraphStageIsland(
   private val logicArrayType = Array.empty[GraphStageLogic]
   private[this] val logics = new ArrayList[GraphStageLogic](64)
   // TODO: Resize
-  private val connections = new Array[Connection](64)
+  private var connections = new Array[Connection](16)
   private var maxConnections = 0
   private var outConnections: List[Connection] = Nil
   private var fullIslandName: OptionVal[String] = OptionVal.None
@@ -613,6 +613,9 @@ final class GraphStageIsland(
 
   def conn(slot: Int): Connection = {
     maxConnections = math.max(slot, maxConnections)
+    if (maxConnections >= connections.length) {
+      connections = connections.padTo(connections.length * 2, null)
+    }
     val c = connections(slot)
     if (c ne null) c
     else {