diff --git a/stream/src/main/scala/org/apache/pekko/stream/javadsl/Flow.scala b/stream/src/main/scala/org/apache/pekko/stream/javadsl/Flow.scala
index 91b0385e49..df395c1ad5 100755
--- a/stream/src/main/scala/org/apache/pekko/stream/javadsl/Flow.scala
+++ b/stream/src/main/scala/org/apache/pekko/stream/javadsl/Flow.scala
@@ -2500,7 +2500,7 @@ final class Flow[In, Out, Mat](delegate: scaladsl.Flow[In, Out, Mat]) extends Gr
    */
   def flatMapPrefix[Out2, Mat2](
       n: Int,
-      f: function.Function[java.lang.Iterable[Out], javadsl.Flow[Out, Out2, Mat2]]): javadsl.Flow[In, Out2, Mat] = {
+      f: function.Function[java.util.List[Out], javadsl.Flow[Out, Out2, Mat2]]): javadsl.Flow[In, Out2, Mat] = {
     val newDelegate = delegate.flatMapPrefix(n)(seq => f(seq.asJava).asScala)
     new javadsl.Flow(newDelegate)
   }
@@ -2511,7 +2511,7 @@ final class Flow[In, Out, Mat](delegate: scaladsl.Flow[In, Out, Mat]) extends Gr
    */
   def flatMapPrefixMat[Out2, Mat2, Mat3](
       n: Int,
-      f: function.Function[java.lang.Iterable[Out], javadsl.Flow[Out, Out2, Mat2]],
+      f: function.Function[java.util.List[Out], javadsl.Flow[Out, Out2, Mat2]],
       matF: function.Function2[Mat, CompletionStage[Mat2], Mat3]): javadsl.Flow[In, Out2, Mat3] = {
     val newDelegate = delegate.flatMapPrefixMat(n)(seq => f(seq.asJava).asScala) { (m1, fm2) =>
       matF(m1, fm2.asJava)
diff --git a/stream/src/main/scala/org/apache/pekko/stream/javadsl/Source.scala b/stream/src/main/scala/org/apache/pekko/stream/javadsl/Source.scala
index bcd289b785..1f50fea255 100755
--- a/stream/src/main/scala/org/apache/pekko/stream/javadsl/Source.scala
+++ b/stream/src/main/scala/org/apache/pekko/stream/javadsl/Source.scala
@@ -3980,7 +3980,7 @@ final class Source[Out, Mat](delegate: scaladsl.Source[Out, Mat]) extends Graph[
    */
   def flatMapPrefix[Out2, Mat2](
       n: Int,
-      f: function.Function[java.lang.Iterable[Out], javadsl.Flow[Out, Out2, Mat2]]): javadsl.Source[Out2, Mat] = {
+      f: function.Function[java.util.List[Out], javadsl.Flow[Out, Out2, Mat2]]): javadsl.Source[Out2, Mat] = {
     val newDelegate = delegate.flatMapPrefix(n)(seq => f(seq.asJava).asScala)
     new javadsl.Source(newDelegate)
   }
@@ -3991,7 +3991,7 @@ final class Source[Out, Mat](delegate: scaladsl.Source[Out, Mat]) extends Graph[
    */
   def flatMapPrefixMat[Out2, Mat2, Mat3](
       n: Int,
-      f: function.Function[java.lang.Iterable[Out], javadsl.Flow[Out, Out2, Mat2]],
+      f: function.Function[java.util.List[Out], javadsl.Flow[Out, Out2, Mat2]],
       matF: function.Function2[Mat, CompletionStage[Mat2], Mat3]): javadsl.Source[Out2, Mat3] = {
     val newDelegate = delegate.flatMapPrefixMat(n)(seq => f(seq.asJava).asScala) { (m1, fm2) =>
       matF(m1, fm2.asJava)
diff --git a/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubFlow.scala b/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubFlow.scala
index 20f73c4f01..37216e02d6 100755
--- a/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubFlow.scala
+++ b/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubFlow.scala
@@ -1761,7 +1761,7 @@ class SubFlow[In, Out, Mat](
    */
   def flatMapPrefix[Out2, Mat2](
       n: Int,
-      f: function.Function[java.lang.Iterable[Out], javadsl.Flow[Out, Out2, Mat2]]): SubFlow[In, Out2, Mat] = {
+      f: function.Function[java.util.List[Out], javadsl.Flow[Out, Out2, Mat2]]): SubFlow[In, Out2, Mat] = {
     val newDelegate = delegate.flatMapPrefix(n)(seq => f(seq.asJava).asScala)
     new javadsl.SubFlow(newDelegate)
   }
diff --git a/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubSource.scala b/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubSource.scala
index 9ac6f9c714..89e676d958 100755
--- a/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubSource.scala
+++ b/stream/src/main/scala/org/apache/pekko/stream/javadsl/SubSource.scala
@@ -1735,7 +1735,7 @@ class SubSource[Out, Mat](
    */
   def flatMapPrefix[Out2, Mat2](
       n: Int,
-      f: function.Function[java.lang.Iterable[Out], javadsl.Flow[Out, Out2, Mat2]]): javadsl.SubSource[Out2, Mat] = {
+      f: function.Function[java.util.List[Out], javadsl.Flow[Out, Out2, Mat2]]): javadsl.SubSource[Out2, Mat] = {
     val newDelegate = delegate.flatMapPrefix(n)(seq => f(seq.asJava).asScala)
     new javadsl.SubSource(newDelegate)
   }