diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/BidiFlow.scala b/akka-stream/src/main/scala/akka/stream/javadsl/BidiFlow.scala
index 88de03067c..dd1bda470c 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/BidiFlow.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/BidiFlow.scala
@@ -88,7 +88,7 @@ object BidiFlow {
     new BidiFlow(scaladsl.BidiFlow.bidirectionalIdleTimeout(timeout))
 }
 
-class BidiFlow[-I1, +O1, -I2, +O2, +Mat](delegate: scaladsl.BidiFlow[I1, O1, I2, O2, Mat]) extends Graph[BidiShape[I1, O1, I2, O2], Mat] {
+final class BidiFlow[-I1, +O1, -I2, +O2, +Mat](delegate: scaladsl.BidiFlow[I1, O1, I2, O2, Mat]) extends Graph[BidiShape[I1, O1, I2, O2], Mat] {
   private[stream] override def module = delegate.module
   override def shape = delegate.shape
 
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/Sink.scala b/akka-stream/src/main/scala/akka/stream/javadsl/Sink.scala
index b53128bb01..f32f024c76 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/Sink.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/Sink.scala
@@ -162,7 +162,7 @@ object Sink {
  * A `Sink` is a set of stream processing steps that has one open input and an attached output.
  * Can be used as a `Subscriber`
  */
-class Sink[-In, +Mat](delegate: scaladsl.Sink[In, Mat]) extends Graph[SinkShape[In], Mat] {
+final class Sink[-In, +Mat](delegate: scaladsl.Sink[In, Mat]) extends Graph[SinkShape[In], Mat] {
 
   override def shape: SinkShape[In] = delegate.shape
   private[stream] def module: StreamLayout.Module = delegate.module
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala b/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
index e04f2eecd5..dba1b1c144 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/Source.scala
@@ -242,7 +242,7 @@ object Source {
  * A `Source` is a set of stream processing steps that has one open output and an attached input.
  * Can be used as a `Publisher`
  */
-class Source[+Out, +Mat](delegate: scaladsl.Source[Out, Mat]) extends Graph[SourceShape[Out], Mat] {
+final class Source[+Out, +Mat](delegate: scaladsl.Source[Out, Mat]) extends Graph[SourceShape[Out], Mat] {
 
   import scala.collection.JavaConverters._