diff --git a/lib/rules/sort-comp.js b/lib/rules/sort-comp.js
index a915280f87..cdb8704156 100644
--- a/lib/rules/sort-comp.js
+++ b/lib/rules/sort-comp.js
@@ -57,7 +57,7 @@ const defaultConfig = {
 function getMethodsOrder(userConfig) {
   userConfig = userConfig || {};
 
-  const groups = Object.assign(defaultConfig.groups, userConfig.groups);
+  const groups = Object.assign({}, defaultConfig.groups, userConfig.groups);
   const order = userConfig.order || defaultConfig.order;
 
   let config = [];