diff --git a/packages/client/src/components/form/folder.vue b/packages/client/src/components/form/folder.vue
index a9d8bd97b8..533ee4bbe6 100644
--- a/packages/client/src/components/form/folder.vue
+++ b/packages/client/src/components/form/folder.vue
@@ -26,10 +26,10 @@ const props = withDefaults(defineProps<{
   defaultOpen: false,
 });
 
-let opened = $ref(props.defaultOpen);
-let openedAtLeastOnce = $ref(props.defaultOpen);
+let opened: boolean = $ref(props.defaultOpen);
+let openedAtLeastOnce: boolean = $ref(props.defaultOpen);
 
-const toggle = () => {
+const toggle = (): void => {
 	opened = !opened;
 	if (opened) {
 		openedAtLeastOnce = true;