diff --git a/src/prepare.js b/src/prepare.js
index 6ece3e8..2314542 100644
--- a/src/prepare.js
+++ b/src/prepare.js
@@ -73,7 +73,7 @@ exports.inherit = config => traverse(config, config, [], (target, key, val, root
             candidates = candidates.concat(parents)
             list.unshift(other)
         }
-        val = extend.apply(this, list)
+        val = extend.apply(null, list)
         delete val.$extends
     }
     target[key] = val