diff --git a/packages/rstack/src/rslibConfig.ts b/packages/rstack/src/rslibConfig.ts
index cf581a1..3faaf14 100644
--- a/packages/rstack/src/rslibConfig.ts
+++ b/packages/rstack/src/rslibConfig.ts
@@ -1,28 +1,24 @@
-import type {
-  ConfigParams,
-  RslibConfig,
-  RslibConfigDefinition,
+import {
+  type ConfigParams,
+  type RslibConfig,
+  type RslibConfigDefinition,
+  mergeRslibConfig,
 } from '@rslib/core';
 import { withConfigMeta } from '@rstackjs/load-config';
 import { loadRstackConfig, type Configs } from './config.ts';
+import { resolveConfigLayers } from './configLayers.ts';
 
-const resolveRslibConfig = async (
-  configs: Configs,
+export const resolveRslibConfig = async (
+  layers: readonly Configs[],
   params: ConfigParams,
 ): Promise<RslibConfig> => {
-  const libConfig = configs.lib;
-  if (!libConfig) {
-    return {};
-  }
-  if (typeof libConfig === 'function') {
-    return libConfig(params);
-  }
-  return libConfig;
+  const configs = await resolveConfigLayers(layers, 'lib', params);
+  return configs.length > 1 ? mergeRslibConfig(...configs) : (configs[0] ?? {});
 };
 
 const loadRslibConfig = (async (params: ConfigParams) => {
   const { configs, filePath, dependencies } = await loadRstackConfig();
-  const config = await resolveRslibConfig(configs, params);
+  const config = await resolveRslibConfig([configs], params);
 
   return withConfigMeta(config, { filePath, dependencies });
 }) as RslibConfigDefinition;
diff --git a/packages/rstack/tests/config/lib-merge.test.ts b/packages/rstack/tests/config/lib-merge.test.ts
new file mode 100644
index 0000000..e9f99c9
--- /dev/null
+++ b/packages/rstack/tests/config/lib-merge.test.ts
@@ -0,0 +1,27 @@
+import { expect, test } from 'rstack/test';
+import { resolveRslibConfig } from '../../src/rslibConfig.ts';
+
+test('merges lib layers using native Rslib rules', async () => {
+  const config = await resolveRslibConfig(
+    [
+      {
+        lib: {
+          source: { define: { SHARED: true, ENV: 'base' } },
+          lib: [{ id: 'esm', format: 'esm', dts: true }],
+        },
+      },
+      {
+        lib: {
+          source: { define: { ENV: 'production' } },
+          lib: [{ id: 'esm', dts: false }, { format: 'cjs' }],
+        },
+      },
+    ],
+    { command: 'build', env: 'production' },
+  );
+
+  expect(config).toEqual({
+    source: { define: { SHARED: true, ENV: 'production' } },
+    lib: [{ id: 'esm', format: 'esm', dts: false }, { format: 'cjs' }],
+  });
+});