diff --git a/packages/resource/src/json-resource.js b/packages/resource/src/json-resource.js
index 3df1b06..76efb90 100644
--- a/packages/resource/src/json-resource.js
+++ b/packages/resource/src/json-resource.js
@@ -10,20 +10,26 @@ export default class JsonResource extends Resource {
   }
 
   static async extendJson(json) {
-    if ('string' === typeof json.extends) {
-      // eslint-disable-next-line no-param-reassign
-      json.extends = await this.read(json.extends);
-    }
-    return this.mergeJson(json);
+    return this.mergeJson(
+      'string' === typeof json.extends
+        ? {
+          ...json,
+          extends: await this.read(json.extends),
+        }
+        : json,
+    );
   }
 
   static async load(json = {}) {
     const resource = new this();
-    if ('string' === typeof json.extends) {
-      // eslint-disable-next-line no-param-reassign
-      json.uri = json.extends;
-    }
-    await resource.load(await this.extendJson(json));
+    await resource.load(await this.extendJson(
+      'string' === typeof json.extends
+        ? {
+          ...json,
+          uri: json.extends,
+        }
+        : json,
+    ));
     return resource;
   }