diff --git a/packages/next/src/build/index.ts b/packages/next/src/build/index.ts
index f19fde79196f5..001a9a4ab0bd0 100644
--- a/packages/next/src/build/index.ts
+++ b/packages/next/src/build/index.ts
@@ -1497,17 +1497,17 @@ export default async function build(
         ? await readManifest<AppBuildManifest>(appBuildManifestPath)
         : undefined
 
-      let appPathsManifest: Record<string, string> = {}
       const appPathRoutes: Record<string, string> = {}
 
       if (appDir) {
-        appPathsManifest = await readManifest(
+        const appPathsManifest = await readManifest<Record<string, string>>(
           path.join(distDir, SERVER_DIRECTORY, APP_PATHS_MANIFEST)
         )
 
-        Object.keys(appPathsManifest).forEach((entry) => {
-          appPathRoutes[entry] = normalizeAppPath(entry)
-        })
+        for (const key in appPathsManifest) {
+          appPathRoutes[key] = normalizeAppPath(key)
+        }
+
         await writeManifest(
           path.join(distDir, APP_PATH_ROUTES_MANIFEST),
           appPathRoutes