diff --git a/README.md b/README.md
index 47f9c9a..1db9e5a 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,17 @@ $ npm i -D @oshx/type-helper
 
 Please add below in `tsconfig.json` file.
 ```json
+{
+  "compilerOptions": {
+    "typeRoots": [
+      "node_modules/@oshx"
+    ]
+  }
+}
+```
+
+If your TypeScript doesn't accept that type, then add below.
+```json
 {
   "compilerOptions": {
     "typeRoots": [
diff --git a/index.d.ts b/index.d.ts
index 0a51dcc..7f31b60 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -32,9 +32,9 @@ declare type ObjectValue<T extends object = any> = T[ObjectKey<T>]
  */
 declare type PropsWithClassName<
   T extends object = object,
-  ClassNameType = string | undefined
+  ClassNameType = string
 > = {
-  className: ClassNameType
+  className?: ClassNameType
 } & T
 
 /** The simple `Any function` declaration.
diff --git a/package.json b/package.json
index 5f5156e..20c1455 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@oshx/type-helper",
-  "version": "1.0.5",
+  "version": "1.0.6",
   "description": "Types help TypeScript types.",
   "repository": {
     "type": "git",