diff --git a/packages/raw-modules/src/index.ts b/packages/raw-modules/src/index.ts
index b53d62e25..62ba02b1f 100644
--- a/packages/raw-modules/src/index.ts
+++ b/packages/raw-modules/src/index.ts
@@ -27,8 +27,8 @@ const rawModules = (conf: Configuration, env: string, options = {} as ReactLibra
   ];
   // Exclude all less files (including module files) from file-loader
   conf.module.rules = conf.module.rules.map((rule) => {
-    if (typeof rule === 'object' && rule.oneOf) {
-      rule.oneOf = loaders.concat(rule.oneOf);
+    if (typeof rule === 'object' && rule.oneOf && Array.isArray(rule.oneOf)) {
+      rule.oneOf = [...loaders, ...rule.oneOf];
     }
     return rule;
   });