diff --git a/types/index.d.ts b/types/index.d.ts
index bdd60567..439dddbf 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -127,7 +127,7 @@ export interface RenderOptions<
    * @see {@link https://react.dev/reference/react-dom/client/createRoot#parameters createRoot#options}
    */
   onCaughtError?: ReactDOMClient.RootOptions extends {
-    onCaughtError: infer OnCaughtError
+    onCaughtError?: infer OnCaughtError
   }
     ? OnCaughtError
     : never
diff --git a/types/test.tsx b/types/test.tsx
index 825d5699..121bc79f 100644
--- a/types/test.tsx
+++ b/types/test.tsx
@@ -266,9 +266,16 @@ export function testContainer() {
 export function testErrorHandlers() {
   // React 19 types are not used in tests. Verify manually if this works with `"@types/react": "npm:types-react@rc"`
   render(null, {
-    // Should work with React 19 types
-    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
-    // @ts-expect-error
+    // Should work with React 19 types but intentionally fails with React 18 types.
+    //
+    // > Why use `@ts-ignore` instead of `@ts-expect-error`?
+    // > Default React 19 types work error-free, causing TS compiler
+    // > to report `@ts-expect-error` as unused (requiring removal).
+    // > But for compatibility with React 18 types in tests,
+    // > we have to use `@ts-ignore` instead.
+    //
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment, @typescript-eslint/prefer-ts-expect-error
+    // @ts-ignore
     onCaughtError: () => {},
   })
   render(null, {