diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSplitWhenSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSplitWhenSpec.scala
index 41906b4468..14eed3d8cc 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSplitWhenSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSplitWhenSpec.scala
@@ -3,14 +3,16 @@
  */
 package akka.stream.scaladsl
 
-import akka.NotUsed
+import akka.{ Done, NotUsed }
 import akka.stream._
 import akka.stream.Supervision.resumingDecider
 import akka.stream.impl.SubscriptionTimeoutException
 import akka.stream.testkit.Utils._
 import akka.stream.testkit._
+import akka.stream.testkit.scaladsl.TestSink
 import org.reactivestreams.Publisher
-import scala.concurrent.Await
+
+import scala.concurrent.{ Await, Future }
 import scala.concurrent.duration._
 
 class FlowSplitWhenSpec extends StreamSpec {
@@ -257,14 +259,19 @@ class FlowSplitWhenSpec extends StreamSpec {
     }
 
     "fail substream if materialized twice" in assertAllStagesStopped {
+      implicit val mat = ActorMaterializer(ActorMaterializerSettings(system)
+        .withInputBuffer(initialSize = 1, maxSize = 1))
+
       import system.dispatcher
+      val probe = Source(1 to 5).splitWhen(_ ⇒ true).lift
+        .map { src ⇒ src.runWith(Sink.ignore)(mat).flatMap(_ ⇒ src.runWith(Sink.ignore)(mat)) }
+        .runWith(TestSink.probe[Future[Done]])(mat)
+      probe.request(1)
+      val future = probe.requestNext()
       an[IllegalStateException] mustBe thrownBy {
-        Await.result(
-          Source.single(1).splitWhen(_ ⇒ true).lift
-            .mapAsync(1) { src ⇒ src.runWith(Sink.ignore).flatMap(_ ⇒ src.runWith(Sink.ignore)) } // Sink.ignore+mapAsync pipes error back
-            .runWith(Sink.ignore),
-          3.seconds)
+        Await.result(future, 3.seconds)
       }
+      probe.cancel()
     }
 
     "fail stream if substream not materialized in time" in assertAllStagesStopped {