diff --git a/docs/src/test/java/jdocs/testkit/TestKitDocTest.java b/docs/src/test/java/jdocs/testkit/TestKitDocTest.java
index e2750baa409..c753a57361d 100644
--- a/docs/src/test/java/jdocs/testkit/TestKitDocTest.java
+++ b/docs/src/test/java/jdocs/testkit/TestKitDocTest.java
@@ -93,7 +93,7 @@ public void demonstrateTestActorRef() {
 
   // #timer
   static class TestTimerActor extends AbstractActorWithTimers {
-    private static String SCHED_KEY = "SchedKey";
+    private static final String SCHED_KEY = "SchedKey";
 
     static final class TriggerScheduling {}
 
@@ -110,7 +110,7 @@ void triggerScheduling() {
   }
 
   static class TestTimerUntypedActor extends UntypedAbstractActorWithTimers {
-    private static String SCHED_KEY = "SchedKey";
+    private static final String SCHED_KEY = "SchedKey";
 
     static final class TriggerScheduling {}