diff --git a/packages/core/src/config.ts b/packages/core/src/config.ts
index b7a990eb9..2fe97babd 100644
--- a/packages/core/src/config.ts
+++ b/packages/core/src/config.ts
@@ -890,7 +890,7 @@ const composeEntryConfig = async (
   root: string,
   cssModulesAuto: CssLoaderOptionsAuto,
 ): Promise<{ entryConfig: EnvironmentConfig; lcp: string | null }> => {
-  let entries = rawEntry;
+  let entries: RsbuildConfigEntry = rawEntry;
 
   if (!entries) {
     // In bundle mode, return directly to let Rsbuild apply default entry to './src/index.ts'
@@ -904,6 +904,15 @@ const composeEntryConfig = async (
     };
   }
 
+  // Type check to ensure entries is of the expected type
+  if (typeof entries !== 'object') {
+    throw new Error(
+      `The ${color.cyan('source.entry')} configuration should be an object, but received ${typeof entries}: ${color.cyan(
+        entries,
+      )}. Checkout ${color.green('https://lib.rsbuild.dev/config/rsbuild/source#sourceentry')} for more details.`,
+    );
+  }
+
   if (bundle !== false) {
     const entryErrorReasons: string[] = [];
     traverseEntryQuery(entries, (entry) => {
diff --git a/tests/integration/entry/index.test.ts b/tests/integration/entry/index.test.ts
index 499b3aad9..62e429246 100644
--- a/tests/integration/entry/index.test.ts
+++ b/tests/integration/entry/index.test.ts
@@ -154,4 +154,17 @@ test('validate entry and throw errors', async () => {
   expect(stripAnsi(errMsg)).toMatchInlineSnapshot(
     `"Error: Can't resolve the entry "./src/main.ts" at the location <ROOT>/tests/integration/entry/validate/src/main.ts. Please ensure that the file exists."`,
   );
+
+  try {
+    await buildAndGetResults({
+      fixturePath,
+      configPath: 'bundlelessWithString.config.ts',
+    });
+  } catch (e) {
+    errMsg = (e as Error).message;
+  }
+
+  expect(stripAnsi(errMsg)).toMatchInlineSnapshot(
+    `"The source.entry configuration should be an object, but received string: ./src/**. Checkout https://lib.rsbuild.dev/config/rsbuild/source#sourceentry for more details."`,
+  );
 });
diff --git a/tests/integration/entry/validate/bundlelessWithString.config.ts b/tests/integration/entry/validate/bundlelessWithString.config.ts
new file mode 100644
index 000000000..265d36787
--- /dev/null
+++ b/tests/integration/entry/validate/bundlelessWithString.config.ts
@@ -0,0 +1,14 @@
+import { defineConfig } from '@rslib/core';
+import { generateBundleEsmConfig } from 'test-helper';
+
+export default defineConfig({
+  lib: [
+    generateBundleEsmConfig({
+      bundle: false,
+      source: {
+        // @ts-expect-error test error config
+        entry: './src/**',
+      },
+    }),
+  ],
+});
diff --git a/website/docs/en/config/rsbuild/source.mdx b/website/docs/en/config/rsbuild/source.mdx
index 35e7e215c..d5ee21ca7 100644
--- a/website/docs/en/config/rsbuild/source.mdx
+++ b/website/docs/en/config/rsbuild/source.mdx
@@ -25,8 +25,22 @@ Used to set the entry modules for building.
 
 In Rslib, the default value is:
 
-- bundle mode: `src/index.(ts|js|tsx|jsx|mjs|cjs)`
-- bundleless mode: `src/**`
+- bundle mode:
+
+```ts
+const defaultEntry = {
+  // default support for other suffixes such as ts, tsx, jsx, mjs, cjs
+  index: 'src/index.js',
+};
+```
+
+- bundleless mode:
+
+```ts
+const defaultEntry = {
+  index: 'src/**',
+};
+```
 
 :::info
 Check out the [lib.bundle](/config/lib/bundle#set-entry) to learn more about how to set entry for bundle and bundleless project.
diff --git a/website/docs/zh/config/rsbuild/source.mdx b/website/docs/zh/config/rsbuild/source.mdx
index 6ec1053d1..068af35ee 100644
--- a/website/docs/zh/config/rsbuild/source.mdx
+++ b/website/docs/zh/config/rsbuild/source.mdx
@@ -24,8 +24,22 @@ import { RsbuildDocBadge } from '@components/RsbuildDocBadge';
 
 在 Rslib 中，默认值为：
 
-- bundle 模式：`src/index.(ts|js|tsx|jsx|mjs|cjs)`
-- bundleless 模式：`src/**`
+- bundle 模式：
+
+```ts
+const defaultEntry = {
+  // 默认支持其他后缀，如 ts、tsx、jsx、mjs、cjs
+  index: 'src/index.js',
+};
+```
+
+- bundleless 模式：
+
+```ts
+const defaultEntry = {
+  index: 'src/**',
+};
+```
 
 :::info
 参考 [lib.bundle](/config/lib/bundle#set-entry) 进一步了解如何为 bundle 和 bundleless 项目设置入口。