diff --git a/lib/config/options/index.ts b/lib/config/options/index.ts
index ae7e810c742205..cdbb0ae6d4a62b 100644
--- a/lib/config/options/index.ts
+++ b/lib/config/options/index.ts
@@ -152,8 +152,7 @@ const options: RenovateOptions[] = [
   },
   {
     name: 'extends',
-    description:
-      'Configuration presets to use/extend. Note: does not work if configured in config.js.',
+    description: 'Configuration presets to use/extend.',
     stage: 'package',
     type: 'array',
     subType: 'string',
diff --git a/lib/workers/repository/init/merge.spec.ts b/lib/workers/repository/init/merge.spec.ts
index 36c7a4076dc9b4..464754b5033ccc 100644
--- a/lib/workers/repository/init/merge.spec.ts
+++ b/lib/workers/repository/init/merge.spec.ts
@@ -185,16 +185,28 @@ describe('workers/repository/init/merge', () => {
     it('migrates nested config', async () => {
       git.getFileList.mockResolvedValue(['renovate.json']);
       fs.readLocalFile.mockResolvedValue('{}');
-      migrateAndValidate.migrateAndValidate.mockResolvedValue({
-        warnings: [],
-        errors: [],
-      });
-      migrate.migrateConfig.mockReturnValueOnce({
+      migrateAndValidate.migrateAndValidate.mockImplementation((_, c) =>
+        Promise.resolve({
+          ...c,
+          warnings: [],
+          errors: [],
+        })
+      );
+      migrate.migrateConfig.mockImplementation((c) => ({
         isMigrated: true,
-        migratedConfig: {},
+        migratedConfig: c,
+      }));
+      config.extends = [':automergeAll'];
+      config.packageRules = [{ extends: ['monorepo:react'] }];
+      const ret = await mergeRenovateConfig(config);
+      expect(ret).toMatchObject({
+        automerge: true,
+        packageRules: [
+          {
+            matchSourceUrlPrefixes: ['https://github.com/facebook/react'],
+          },
+        ],
       });
-      config.extends = [':automergeDisabled'];
-      expect(await mergeRenovateConfig(config)).toBeDefined();
     });
     it('continues if no errors', async () => {
       git.getFileList.mockResolvedValue(['package.json', '.renovaterc.json']);
diff --git a/lib/workers/repository/init/merge.ts b/lib/workers/repository/init/merge.ts
index 701697a7660fde..d603978a6b1900 100644
--- a/lib/workers/repository/init/merge.ts
+++ b/lib/workers/repository/init/merge.ts
@@ -177,6 +177,13 @@ export async function mergeRenovateConfig(
     ];
     delete returnConfig.extends;
   }
+  if (is.nonEmptyArray(returnConfig.packageRules)) {
+    configFileParsed.packageRules = [
+      ...returnConfig.packageRules,
+      ...(configFileParsed.packageRules || []),
+    ];
+    delete returnConfig.packageRules;
+  }
   checkForRepoConfigError(repoConfig);
   const migratedConfig = await migrateAndValidate(config, configFileParsed);
   if (migratedConfig.errors.length) {