diff --git a/src/packages/StorageFileApi.ts b/src/packages/StorageFileApi.ts
index 1f9417e..7411fd1 100644
--- a/src/packages/StorageFileApi.ts
+++ b/src/packages/StorageFileApi.ts
@@ -40,7 +40,7 @@ type FileBody =
 export default class StorageFileApi {
   protected url: string
   protected headers: { [key: string]: string }
-  protected bucketId?: string
+  protected bucketId: string | undefined
   protected fetch: Fetch
 
   constructor(
diff --git a/tsconfig.json b/tsconfig.json
index ac82271..e202dd4 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -11,6 +11,7 @@
     "target": "ES6",
 
     "strict": true,
+    "exactOptionalPropertyTypes": true,
 
     "esModuleInterop": true,
     "moduleResolution": "Node",