diff --git a/stub/src/main/java/org/apache/commons/proxy2/stub/StubInterceptorBuilder.java b/stub/src/main/java/org/apache/commons/proxy2/stub/StubInterceptorBuilder.java
index af0e64e..35fc206 100644
--- a/stub/src/main/java/org/apache/commons/proxy2/stub/StubInterceptorBuilder.java
+++ b/stub/src/main/java/org/apache/commons/proxy2/stub/StubInterceptorBuilder.java
@@ -64,7 +64,7 @@
 // Inner Classes
 //----------------------------------------------------------------------------------------------------------------------
 
-    private static class TrainingContextInvoker implements Invoker
+    private static final class TrainingContextInvoker implements Invoker
     {
         private final TrainingContext trainingContext;