diff --git a/src/frontend/src/features/sdk/utils/CallbackIdHandler.ts b/src/frontend/src/features/sdk/utils/CallbackIdHandler.ts
index 1e071eb9..aeee0736 100644
--- a/src/frontend/src/features/sdk/utils/CallbackIdHandler.ts
+++ b/src/frontend/src/features/sdk/utils/CallbackIdHandler.ts
@@ -1,5 +1,5 @@
 export class CallbackIdHandler {
-  private storageKey = 'popup_callback_id'
+  private readonly storageKey = 'popup_callback_id'
 
   private generateId(): string {
     return (