diff --git a/packages/vite-plugin-mock/src/createMockServer.ts b/packages/vite-plugin-mock/src/createMockServer.ts
index c092734..c27b4d0 100644
--- a/packages/vite-plugin-mock/src/createMockServer.ts
+++ b/packages/vite-plugin-mock/src/createMockServer.ts
@@ -88,8 +88,8 @@ export async function requestMiddleware(opt: ViteMockOptions) {
       } else {
         const body = await parseJson(req)
         res.setHeader('Content-Type', 'application/json')
-        if (opt) {
-          res.setHeader('Access-Control-Allow-Credentials', true)
+        if (opt.cors) {
+          res.setHeader('Access-Control-Allow-Credentials', 'true')
           res.setHeader('Access-Control-Allow-Origin', req.headers.origin || '*')
         }
         res.statusCode = statusCode || 200