diff --git a/stream/src/main/scala/org/apache/pekko/stream/impl/PhasedFusingActorMaterializer.scala b/stream/src/main/scala/org/apache/pekko/stream/impl/PhasedFusingActorMaterializer.scala
index fc5b35bd1c..96033f26ed 100644
--- a/stream/src/main/scala/org/apache/pekko/stream/impl/PhasedFusingActorMaterializer.scala
+++ b/stream/src/main/scala/org/apache/pekko/stream/impl/PhasedFusingActorMaterializer.scala
@@ -60,7 +60,7 @@ import org.reactivestreams.Subscriber
  */
 @InternalApi private[pekko] object PhasedFusingActorMaterializer {
 
-  val Debug = false
+  final val Debug = false
 
   val MailboxConfigName: String = "pekko.stream.materializer.mailbox"