diff --git a/packages/next/next-server/lib/router/router.ts b/packages/next/next-server/lib/router/router.ts
index c4ef80b224d5d..627c94f5bd663 100644
--- a/packages/next/next-server/lib/router/router.ts
+++ b/packages/next/next-server/lib/router/router.ts
@@ -17,8 +17,7 @@ import { isDynamicRoute } from './utils/is-dynamic'
 import { getRouteMatcher } from './utils/route-matcher'
 import { getRouteRegex } from './utils/route-regex'
 
-// @ts-ignore variable is always a string
-const basePath: string = process.env.__NEXT_ROUTER_BASEPATH
+const basePath = process.env.__NEXT_ROUTER_BASEPATH as string
 
 export function addBasePath(path: string): string {
   return path.indexOf(basePath) !== 0 ? basePath + path : path