diff --git a/src/index.ts b/src/index.ts
index 562e2d7..9075df0 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -39,7 +39,7 @@ export default function webExtension(
     configureServer(server) {
       server.middlewares.use(viteClientModifier);
 
-      server.httpServer!.once("listening", () => {
+      server.httpServer?.once("listening", () => {
         manifestParser.setDevServer(server);
         manifestParser.writeDevBuild(server.config.server.port!);
       });