diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowPrefixAndTailSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowPrefixAndTailSpec.scala
index 066b1eba75..a42ac62eb4 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowPrefixAndTailSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowPrefixAndTailSpec.scala
@@ -92,21 +92,25 @@ class FlowPrefixAndTailSpec extends StreamSpec("""
 
     "throw if tail is attempted to be materialized twice" in assertAllStagesStopped {
       val futureSink = newHeadSink
-      val fut = Source(1 to 2).prefixAndTail(1).runWith(futureSink)
-      val (takes, tail) = Await.result(fut, 3.seconds)
-      takes should be(Seq(1))
+      val fut = Source(1 to 3).prefixAndTail(1).runWith(futureSink)
+      val (prefix, tail) = Await.result(fut, 3.seconds)
+      prefix should be(Seq(1))
 
       val subscriber1 = TestSubscriber.probe[Int]()
       tail.to(Sink.fromSubscriber(subscriber1)).run()
+      // make sure it was materialized once before ...
+      subscriber1.ensureSubscription()
+      subscriber1.request(1)
+      subscriber1.expectNext(2)
 
+      // ... verifying what happens on a second materialization
       val subscriber2 = TestSubscriber.probe[Int]()
       tail.to(Sink.fromSubscriber(subscriber2)).run()
       val ex = subscriber2.expectSubscriptionAndError()
       ex.getMessage should ===("Substream Source(TailSource) cannot be materialized more than once")
       ex.getStackTrace.exists(_.getClassName contains "FlowPrefixAndTailSpec") shouldBe true
 
-      subscriber1.requestNext(2).expectComplete()
-
+      subscriber1.requestNext(3).expectComplete()
     }
 
     "signal error if substream has been not subscribed in time" in assertAllStagesStopped {