diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSlidingSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSlidingSpec.scala
index 77324635e7..c8414eeaa6 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSlidingSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowSlidingSpec.scala
@@ -3,128 +3,54 @@
  */
 package akka.stream.scaladsl
 
-import akka.actor.ActorSystem
 import akka.stream.testkit.Utils._
-import akka.stream.testkit.scaladsl.TestSink
 import akka.stream.{ ActorMaterializer, ActorMaterializerSettings }
 import akka.stream.testkit._
-import com.typesafe.config.ConfigFactory
+import org.scalacheck.Gen
+import org.scalatest.prop.GeneratorDrivenPropertyChecks
+import akka.pattern.pipe
+
 import scala.concurrent.Await
-import scala.concurrent.duration._
 
-class FlowSlidingSpec extends AkkaSpec {
+class FlowSlidingSpec extends AkkaSpec with GeneratorDrivenPropertyChecks {
   import system.dispatcher
-  val settings = ActorMaterializerSettings(system)
-    .withInputBuffer(initialSize = 2, maxSize = 16)
-
-  implicit val mat = ActorMaterializer(settings)
-
+  implicit val mat = ActorMaterializer(ActorMaterializerSettings(system))
   "Sliding" must {
-    "work with n = 3, step = 1" in assertAllStagesStopped {
-      Source(1 to 6).sliding(n = 3, step = 1).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
+    import org.scalacheck.Shrink.shrinkAny
+    def check(gen: Gen[(Int, Int, Int)]): Unit =
+      forAll(gen, MinSize(1000), MaxSize(1000)) {
+        case (len, win, step) ⇒
+          val af = Source(() ⇒ Iterator.from(0).take(len)).sliding(win, step).runFold(Seq.empty[Seq[Int]])(_ :+ _)
+          val cf = Source(() ⇒ Iterator.from(0).take(len).sliding(win, step)).runFold(Seq.empty[Seq[Int]])(_ :+ _)
+          Await.result(af, remaining) should be(Await.result(cf, remaining))
       }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(2, 3, 4))
-      expectMsg(Vector(3, 4, 5))
-      expectMsg(Vector(4, 5, 6))
-      expectMsg("done")
+
+    "behave just like collections sliding with step < window" in assertAllStagesStopped {
+      check(for {
+        len ← Gen.choose(0, 31)
+        win ← Gen.choose(1, 61)
+        step ← Gen.choose(1, win - 1)
+      } yield (len, win, step))
     }
 
-    "work with n = 3, step = 1, 7 elements" in assertAllStagesStopped {
-      Source(1 to 7).sliding(n = 3, step = 1).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(2, 3, 4))
-      expectMsg(Vector(3, 4, 5))
-      expectMsg(Vector(4, 5, 6))
-      expectMsg(Vector(5, 6, 7))
-      expectMsg("done")
+    "behave just like collections sliding with step == window" in assertAllStagesStopped {
+      check(for {
+        len ← Gen.choose(0, 31)
+        win ← Gen.choose(1, 61)
+        step ← Gen.const(win)
+      } yield (len, win, step))
     }
 
-    "work with n = 3, step = 2" in assertAllStagesStopped {
-      Source(1 to 6).sliding(n = 3, step = 2).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(3, 4, 5))
-      expectMsg(Vector(5, 6))
-      expectMsg("done")
-    }
-
-    "work with n = 3, step = 2, complete group" in assertAllStagesStopped {
-      Source(1 to 7).sliding(n = 3, step = 2).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(3, 4, 5))
-      expectMsg(Vector(5, 6, 7))
-      expectMsg("done")
-    }
-
-    "work with n = 3, step = 3" in assertAllStagesStopped {
-      Source(1 to 6).sliding(n = 3, step = 3).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(4, 5, 6))
-      expectMsg("done")
-    }
-
-    "work with n = 2, step = 3" in assertAllStagesStopped {
-      Source(1 to 6).sliding(n = 2, step = 3).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2))
-      expectMsg(Vector(4, 5))
-      expectMsg("done")
-    }
-
-    "work with n = 2, step = 1" in assertAllStagesStopped {
-      Source(1 to 6).sliding(n = 2, step = 1).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2))
-      expectMsg(Vector(2, 3))
-      expectMsg(Vector(3, 4))
-      expectMsg(Vector(4, 5))
-      expectMsg(Vector(5, 6))
-      expectMsg("done")
-    }
-
-    "work with n = 3, step = 4" in assertAllStagesStopped {
-      Source(1 to 12).sliding(n = 3, step = 4).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(5, 6, 7))
-      expectMsg(Vector(9, 10, 11))
-      expectMsg("done")
-    }
-
-    "work with n = 3, step = 6" in assertAllStagesStopped {
-      Source(1 to 12).sliding(n = 3, step = 6).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(7, 8, 9))
-      expectMsg("done")
-    }
-
-    "work with n = 3, step = 10, incomplete group" in assertAllStagesStopped {
-      Source(1 to 12).sliding(n = 3, step = 10).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
-      expectMsg(Vector(1, 2, 3))
-      expectMsg(Vector(11, 12))
-      expectMsg("done")
+    "behave just like collections sliding with step > window" in assertAllStagesStopped {
+      check(for {
+        len ← Gen.choose(0, 31)
+        win ← Gen.choose(1, 61)
+        step ← Gen.choose(win + 1, 127)
+      } yield (len, win, step))
     }
 
     "work with empty sources" in assertAllStagesStopped {
-      Source.empty.sliding(1).runForeach(testActor ! _) onSuccess {
-        case _ ⇒ testActor ! "done"
-      }
+      Source.empty.sliding(1).runForeach(testActor ! _).map(_ ⇒ "done") pipeTo testActor
       expectMsg("done")
     }
   }
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala
index 2dc1437da3..8ef091e4c7 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala
@@ -318,55 +318,32 @@ private[akka] final case class Grouped[T](n: Int) extends PushPullStage[T, immut
  * INTERNAL API
  */
 private[akka] final case class Sliding[T](n: Int, step: Int) extends PushPullStage[T, immutable.Seq[T]] {
-  private val buf = {
-    val b = Vector.newBuilder[T]
-    b.sizeHint(n)
-    b
-  }
-  var bufferedElements = 0
+  private var buf = Vector.empty[T]
 
   override def onPush(elem: T, ctx: Context[immutable.Seq[T]]): SyncDirective = {
-    buf += elem
-    bufferedElements += 1
-    if (bufferedElements < n) {
+    buf :+= elem
+    if (buf.size < n) {
+      ctx.pull()
+    } else if (buf.size == n) {
+      ctx.push(buf)
+    } else if (step > n) {
+      if (buf.size == step)
+        buf = Vector.empty
       ctx.pull()
-    } else if (bufferedElements == n) {
-      ctx.push(buf.result())
     } else {
-      if (step > n) {
-        if (bufferedElements == step) {
-          buf.clear()
-          buf.sizeHint(n)
-          bufferedElements = 0
-          ctx.pull()
-        } else {
-          ctx.pull()
-        }
-      } else {
-        val emit = buf.result()
-        buf.clear()
-        buf.sizeHint(n)
-        emit.drop(step).foreach(buf += _)
-        val updatedEmit = buf.result()
-        bufferedElements = updatedEmit.size
-        if (bufferedElements == n) ctx.push(updatedEmit)
-        else ctx.pull()
-      }
+      buf = buf.drop(step)
+      if (buf.size == n) ctx.push(buf)
+      else ctx.pull()
     }
   }
 
   override def onPull(ctx: Context[immutable.Seq[T]]): SyncDirective =
-    if (ctx.isFinishing) {
-      val emit = buf.result()
-      if (emit.size == n) {
-        ctx.finish()
-      } else {
-        ctx.pushAndFinish(emit)
-      }
-    } else ctx.pull()
+    if (!ctx.isFinishing) ctx.pull()
+    else if (buf.size >= n) ctx.finish()
+    else ctx.pushAndFinish(buf)
 
   override def onUpstreamFinish(ctx: Context[immutable.Seq[T]]): TerminationDirective =
-    if (buf.result().isEmpty) ctx.finish()
+    if (buf.isEmpty) ctx.finish()
     else ctx.absorbTermination()
 }