diff --git a/packages/vite/src/node/utils.ts b/packages/vite/src/node/utils.ts
index c6ef88a4cb72fc..7a682a6cfb3373 100644
--- a/packages/vite/src/node/utils.ts
+++ b/packages/vite/src/node/utils.ts
@@ -1100,7 +1100,7 @@ function mergeConfigRecursively(
     }
 
     if (Array.isArray(existing) || Array.isArray(value)) {
-      merged[key] = [...arraify(existing ?? []), ...arraify(value ?? [])]
+      merged[key] = [...arraify(existing), ...arraify(value)]
       continue
     }
     if (isObject(existing) && isObject(value)) {