diff --git a/internal/provider/kubernetes/controller.go b/internal/provider/kubernetes/controller.go
index 5e4fd6668ee..cc94895ad15 100644
--- a/internal/provider/kubernetes/controller.go
+++ b/internal/provider/kubernetes/controller.go
@@ -520,23 +520,7 @@ func addReferenceGrantIndexers(ctx context.Context, mgr manager.Manager) error {
 //     `.spec.rules[].filters`. This helps in querying for HTTPRoutes that are affected by a
 //     particular AuthenticationFilter CRUD.
 func addHTTPRouteIndexers(ctx context.Context, mgr manager.Manager) error {
-	if err := mgr.GetFieldIndexer().IndexField(ctx, &gwapiv1b1.HTTPRoute{}, gatewayHTTPRouteIndex, func(rawObj client.Object) []string {
-		httproute := rawObj.(*gwapiv1b1.HTTPRoute)
-		var gateways []string
-		for _, parent := range httproute.Spec.ParentRefs {
-			if string(*parent.Kind) == gatewayapi.KindGateway {
-				// If an explicit Gateway namespace is not provided, use the HTTPRoute namespace to
-				// lookup the provided Gateway Name.
-				gateways = append(gateways,
-					types.NamespacedName{
-						Namespace: gatewayapi.NamespaceDerefOr(parent.Namespace, httproute.Namespace),
-						Name:      string(parent.Name),
-					}.String(),
-				)
-			}
-		}
-		return gateways
-	}); err != nil {
+	if err := mgr.GetFieldIndexer().IndexField(ctx, &gwapiv1b1.HTTPRoute{}, gatewayHTTPRouteIndex, gatewayHTTPRouteIndexFunc); err != nil {
 		return err
 	}
 
@@ -550,7 +534,7 @@ func addHTTPRouteIndexers(ctx context.Context, mgr manager.Manager) error {
 		for _, rule := range httproute.Spec.Rules {
 			for i := range rule.Filters {
 				filter := rule.Filters[i]
-				if filter.Type == gwapiv1a2.HTTPRouteFilterExtensionRef {
+				if filter.Type == gwapiv1b1.HTTPRouteFilterExtensionRef {
 					if err := gatewayapi.ValidateHTTPRouteFilter(&filter); err != nil {
 						filters = append(filters,
 							types.NamespacedName{
@@ -570,6 +554,24 @@ func addHTTPRouteIndexers(ctx context.Context, mgr manager.Manager) error {
 	return nil
 }
 
+func gatewayHTTPRouteIndexFunc(rawObj client.Object) []string {
+	httproute := rawObj.(*gwapiv1b1.HTTPRoute)
+	var gateways []string
+	for _, parent := range httproute.Spec.ParentRefs {
+		if parent.Kind == nil || string(*parent.Kind) == gatewayapi.KindGateway {
+			// If an explicit Gateway namespace is not provided, use the HTTPRoute namespace to
+			// lookup the provided Gateway Name.
+			gateways = append(gateways,
+				types.NamespacedName{
+					Namespace: gatewayapi.NamespaceDerefOr(parent.Namespace, httproute.Namespace),
+					Name:      string(parent.Name),
+				}.String(),
+			)
+		}
+	}
+	return gateways
+}
+
 func serviceHTTPRouteIndexFunc(rawObj client.Object) []string {
 	httproute := rawObj.(*gwapiv1b1.HTTPRoute)
 	var services []string
diff --git a/internal/provider/kubernetes/routes_test.go b/internal/provider/kubernetes/routes_test.go
index ed30490dd78..a513acd358a 100644
--- a/internal/provider/kubernetes/routes_test.go
+++ b/internal/provider/kubernetes/routes_test.go
@@ -211,7 +211,11 @@ func TestProcessHTTPRoutes(t *testing.T) {
 			for _, filter := range tc.filters {
 				objs = append(objs, filter)
 			}
-			r.client = fakeclient.NewClientBuilder().WithScheme(envoygateway.GetScheme()).WithObjects(objs...).Build()
+			r.client = fakeclient.NewClientBuilder().
+				WithScheme(envoygateway.GetScheme()).
+				WithObjects(objs...).
+				WithIndex(&gwapiv1b1.HTTPRoute{}, gatewayHTTPRouteIndex, gatewayHTTPRouteIndexFunc).
+				Build()
 
 			// Process the test case httproutes.
 			resourceTree := gatewayapi.NewResources()