diff --git a/akka-docs/src/test/java/jdocs/stream/operators/flow/StatefulMapConcat.java b/akka-docs/src/test/java/jdocs/stream/operators/flow/StatefulMapConcat.java
index 5195f02c65..13a17dadbd 100644
--- a/akka-docs/src/test/java/jdocs/stream/operators/flow/StatefulMapConcat.java
+++ b/akka-docs/src/test/java/jdocs/stream/operators/flow/StatefulMapConcat.java
@@ -57,7 +57,7 @@ public class StatefulMapConcat {
 
                   return (element) -> {
                     if (element.startsWith("deny:")) {
-                      denyList.add(element.substring(10));
+                      denyList.add(element.substring("deny:".length()));
                       return Collections
                           .emptyList(); // no element downstream when adding a deny listed keyword
                     } else if (denyList.contains(element)) {
diff --git a/akka-docs/src/test/scala/docs/stream/operators/flow/StatefulMapConcat.scala b/akka-docs/src/test/scala/docs/stream/operators/flow/StatefulMapConcat.scala
index 6f6469397b..78a553f6c1 100644
--- a/akka-docs/src/test/scala/docs/stream/operators/flow/StatefulMapConcat.scala
+++ b/akka-docs/src/test/scala/docs/stream/operators/flow/StatefulMapConcat.scala
@@ -44,7 +44,7 @@ class StatefulMapConcat {
 
       { element =>
         if (element.startsWith("deny:")) {
-          denyList += element.drop(10)
+          denyList += element.drop("deny:".size)
           Nil // no element downstream when adding a deny listed keyword
         } else if (denyList(element)) {
           Nil // no element downstream if element is deny listed