diff --git a/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sClusterGenericStub.java b/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sClusterGenericStub.java
index af87af2..6b5fd7e 100644
--- a/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sClusterGenericStub.java
+++ b/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sClusterGenericStub.java
@@ -240,6 +240,7 @@ public class K8sClusterGenericStub<O extends KubernetesObject,
      * @param <L> the object list type
      * @param <R> the result type
      */
+    @FunctionalInterface
     public interface GenericSupplier<O extends KubernetesObject,
             L extends KubernetesListObject,
             R extends K8sClusterGenericStub<O, L>> {
diff --git a/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sGenericStub.java b/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sGenericStub.java
index b8f1992..aef791f 100644
--- a/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sGenericStub.java
+++ b/org.jdrupes.vmoperator.common/src/org/jdrupes/vmoperator/common/K8sGenericStub.java
@@ -359,6 +359,7 @@ public class K8sGenericStub<O extends KubernetesObject,
      * @param <L> the object list type
      * @param <R> the result type
      */
+    @FunctionalInterface
     public interface GenericSupplier<O extends KubernetesObject,
             L extends KubernetesListObject, R extends K8sGenericStub<O, L>> {