diff --git a/src/index.ts b/src/index.ts
index 6a9ac57..481263f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -66,7 +66,7 @@ export default class PixivApp<CamelcaseKeys extends boolean = true> {
   constructor(
     username?: string,
     password?: string,
-    options?: { camelcaseKeys: CamelcaseKeys }
+    options?: { camelcaseKeys?: CamelcaseKeys }
   ) {
     this.username = username
     this.password = password