diff --git a/packages/nuxt/src/app/config.ts b/packages/nuxt/src/app/config.ts
index 9c1c930d64..78fa433c8e 100644
--- a/packages/nuxt/src/app/config.ts
+++ b/packages/nuxt/src/app/config.ts
@@ -26,6 +26,7 @@ function deepAssign (obj: any, newObj: any) {
   for (const key in newObj) {
     const val = newObj[key]
     if (val !== null && typeof val === 'object') {
+      obj[key] = obj[key] || {}
       deepAssign(obj[key], val)
     } else {
       obj[key] = val