diff --git a/akka-docs/src/test/java/jdocs/tutorial_5/DeviceGroup.java b/akka-docs/src/test/java/jdocs/tutorial_5/DeviceGroup.java
index d0e54c4e72..9ba4b1f6ea 100644
--- a/akka-docs/src/test/java/jdocs/tutorial_5/DeviceGroup.java
+++ b/akka-docs/src/test/java/jdocs/tutorial_5/DeviceGroup.java
@@ -139,8 +139,14 @@ public class DeviceGroup extends AbstractActor {
   //#query-added
 
   private void onAllTemperatures(RequestAllTemperatures r) {
+    // since Java collections are mutable, we want to avoid sharing them between actors (since multiple Actors (threads)
+    // modifying the same mutable data-structure is not safe), and perform a defensive copy of the mutable map:
+    //
+    // Feel free to use your favourite immutable data-structures library with Akka in Java applications!
+    Map<ActorRef, String> actorToDeviceIdCopy = new HashMap<>(this.actorToDeviceId);
+
     getContext().actorOf(DeviceGroupQuery.props(
-            actorToDeviceId, r.requestId, getSender(), new FiniteDuration(3, TimeUnit.SECONDS)));
+        actorToDeviceIdCopy, r.requestId, getSender(), new FiniteDuration(3, TimeUnit.SECONDS)));
   }
 
   @Override
diff --git a/akka-docs/src/test/java/jdocs/tutorial_6/DeviceGroup.java b/akka-docs/src/test/java/jdocs/tutorial_6/DeviceGroup.java
index eed2161331..dfe856f5dd 100644
--- a/akka-docs/src/test/java/jdocs/tutorial_6/DeviceGroup.java
+++ b/akka-docs/src/test/java/jdocs/tutorial_6/DeviceGroup.java
@@ -133,8 +133,14 @@ public class DeviceGroup extends AbstractActor {
   }
 
   private void onAllTemperatures(RequestAllTemperatures r) {
+    // since Java collections are mutable, we want to avoid sharing them between actors (since multiple Actors (threads)
+    // modifying the same mutable data-structure is not safe), and perform a defensive copy of the mutable map:
+    //
+    // Feel free to use your favourite immutable data-structures library with Akka in Java applications!
+    Map<ActorRef, String> actorToDeviceIdCopy = new HashMap<>(this.actorToDeviceId);
+
     getContext().actorOf(DeviceGroupQuery.props(
-            actorToDeviceId, r.requestId, getSender(), new FiniteDuration(3, TimeUnit.SECONDS)));
+            actorToDeviceIdCopy, r.requestId, getSender(), new FiniteDuration(3, TimeUnit.SECONDS)));
   }
 
   @Override