diff --git a/api/v1beta1/index/cluster.go b/api/v1beta1/index/cluster.go
index 226145db9753..09fa67cb2ec5 100644
--- a/api/v1beta1/index/cluster.go
+++ b/api/v1beta1/index/cluster.go
@@ -51,7 +51,7 @@ func ByClusterClassName(ctx context.Context, mgr ctrl.Manager) error {
 func ByClusterClassNamespace(ctx context.Context, mgr ctrl.Manager) error {
 	if err := mgr.GetCache().IndexField(ctx, &clusterv1.Cluster{},
 		ClusterClassNamespaceField,
-		ClusterByClusterClassClassNamespace,
+		ClusterByClusterClassNamespace,
 	); err != nil {
 		return errors.Wrap(err, "error setting index field")
 	}
@@ -70,11 +70,14 @@ func ClusterByClusterClassClassName(o client.Object) []string {
 	return nil
 }
 
-// ClusterByClusterClassClassNamespace contains the logic to index Clusters by ClusterClass namespace.
-func ClusterByClusterClassClassNamespace(o client.Object) []string {
+// ClusterByClusterClassNamespace contains the logic to index Clusters by ClusterClass namespace.
+func ClusterByClusterClassNamespace(o client.Object) []string {
 	cluster, ok := o.(*clusterv1.Cluster)
 	if !ok {
 		panic(fmt.Sprintf("Expected Cluster but got a %T", o))
 	}
-	return []string{cluster.GetClassKey().Namespace}
+	if cluster.Spec.Topology != nil {
+		return []string{cluster.GetClassKey().Namespace}
+	}
+	return nil
 }
diff --git a/docs/book/src/tasks/experimental-features/cluster-class/write-clusterclass.md b/docs/book/src/tasks/experimental-features/cluster-class/write-clusterclass.md
index 990d638888b6..6cca507457ac 100644
--- a/docs/book/src/tasks/experimental-features/cluster-class/write-clusterclass.md
+++ b/docs/book/src/tasks/experimental-features/cluster-class/write-clusterclass.md
@@ -477,7 +477,7 @@ Changing `classNamespace` is not supported in rebase procedure, while changing `
 
 #### Securing cross-namespace reference to the ClusterClass
 
-It is often desirable to restrict free cross-namespace `ClusterClass` access for the `Cluster` object. This can be implemented by defining a [`ValidatingAdmissionPolicy`](https://kubernetes.io/docs/reference/access-authn-authz/validating-admission-policy/) on the `Cluster` object.
+It is often desirable to restrict free cross-namespace `ClusterClass` access for the `Cluster` object. This can be implemented by defining a [ValidatingAdmissionPolicy](https://kubernetes.io/docs/reference/access-authn-authz/validating-admission-policy/#what-is-validating-admission-policy) on the `Cluster` object.
 
 An example of such policy may be:
 
diff --git a/internal/webhooks/clusterclass_test.go b/internal/webhooks/clusterclass_test.go
index 639b9dc71643..6275a271da7b 100644
--- a/internal/webhooks/clusterclass_test.go
+++ b/internal/webhooks/clusterclass_test.go
@@ -92,7 +92,7 @@ func TestClusterClassDefaultNamespaces(t *testing.T) {
 	fakeClient := fake.NewClientBuilder().
 		WithScheme(fakeScheme).
 		WithIndex(&clusterv1.Cluster{}, index.ClusterClassNameField, index.ClusterByClusterClassClassName).
-		WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassClassNamespace).
+		WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassNamespace).
 		Build()
 
 	// Create the webhook and add the fakeClient as its client.
@@ -1867,7 +1867,7 @@ func TestClusterClassValidation(t *testing.T) {
 			fakeClient := fake.NewClientBuilder().
 				WithScheme(fakeScheme).
 				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNameField, index.ClusterByClusterClassClassName).
-				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassClassNamespace).
+				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassNamespace).
 				Build()
 
 			// Pin the compatibility version used in variable CEL validation to 1.29, so we don't have to continuously refactor
@@ -2515,7 +2515,7 @@ func TestClusterClassValidationWithClusterAwareChecks(t *testing.T) {
 				WithScheme(fakeScheme).
 				WithObjects(tt.clusters...).
 				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNameField, index.ClusterByClusterClassClassName).
-				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassClassNamespace).
+				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassNamespace).
 				Build()
 
 			// Create the webhook and add the fakeClient as its client.
@@ -2569,7 +2569,7 @@ func TestGetClustersUsingClusterClass(t *testing.T) {
 				WithScheme(fakeScheme).
 				WithObjects(tt.clusters...).
 				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNameField, index.ClusterByClusterClassClassName).
-				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassClassNamespace).
+				WithIndex(&clusterv1.Cluster{}, index.ClusterClassNamespaceField, index.ClusterByClusterClassNamespace).
 				Build()
 
 			// Create the webhook and add the fakeClient as its client.