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)