diff --git a/packages/vite/src/node/__tests__/build.spec.ts b/packages/vite/src/node/__tests__/build.spec.ts
index 8f4e8f5455056c..d0a9750763c055 100644
--- a/packages/vite/src/node/__tests__/build.spec.ts
+++ b/packages/vite/src/node/__tests__/build.spec.ts
@@ -410,16 +410,15 @@ describe('resolveLibFilename', () => {
   })
 
   test('missing filename', () => {
-    expect(() => {
-      resolveLibFilename(
-        {
-          entry: 'mylib.js',
-        },
-        'es',
-        'myLib',
-        resolve(__dirname, 'packages/noname'),
-      )
-    }).toThrow()
+    const filename = resolveLibFilename(
+      {
+        entry: 'mylib.js',
+      },
+      'es',
+      'myLib',
+      resolve(__dirname, 'packages/noname'),
+    )
+    expect(filename).toBe('named-testing-package.mjs')
   })
 
   test('commonjs package extensions', () => {
diff --git a/packages/vite/src/node/__tests__/packages/module/package.json b/packages/vite/src/node/__tests__/packages/module/package.json
index 3dbc1ca591c055..67756e1d2c410e 100644
--- a/packages/vite/src/node/__tests__/packages/module/package.json
+++ b/packages/vite/src/node/__tests__/packages/module/package.json
@@ -1,3 +1,4 @@
 {
+  "name": "mylib",
   "type": "module"
 }
diff --git a/packages/vite/src/node/__tests__/packages/package.json b/packages/vite/src/node/__tests__/packages/package.json
new file mode 100644
index 00000000000000..bd6442dcacf7c9
--- /dev/null
+++ b/packages/vite/src/node/__tests__/packages/package.json
@@ -0,0 +1,3 @@
+{
+  "name": "named-testing-package"
+}
diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index 2224297146c318..c3012e68a12d34 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -60,7 +60,7 @@ import { dataURIPlugin } from './plugins/dataUri'
 import { buildImportAnalysisPlugin } from './plugins/importAnalysisBuild'
 import { ssrManifestPlugin } from './ssr/ssrManifestPlugin'
 import { buildLoadFallbackPlugin } from './plugins/loadFallback'
-import { findNearestPackageData } from './packages'
+import { findNearestMainPackageData, findNearestPackageData } from './packages'
 import type { PackageCache } from './packages'
 import {
   getResolvedOutDirs,
@@ -919,7 +919,7 @@ export function resolveLibFilename(
     return libOptions.fileName(format, entryName)
   }
 
-  const packageJson = findNearestPackageData(root, packageCache)?.data
+  const packageJson = findNearestMainPackageData(root, packageCache)?.data
   const name =
     libOptions.fileName ||
     (packageJson && typeof libOptions.entry === 'string'
diff --git a/packages/vite/src/node/plugins/css.ts b/packages/vite/src/node/plugins/css.ts
index 40c6ff6aa6e159..27f18bbac7f42e 100644
--- a/packages/vite/src/node/plugins/css.ts
+++ b/packages/vite/src/node/plugins/css.ts
@@ -91,7 +91,7 @@ import type { TransformPluginContext } from '../server/pluginContainer'
 import { searchForWorkspaceRoot } from '../server/searchRoot'
 import { type DevEnvironment } from '..'
 import type { PackageCache } from '../packages'
-import { findNearestPackageData } from '../packages'
+import { findNearestMainPackageData } from '../packages'
 import { addToHTMLProxyTransformResult } from './html'
 import {
   assetUrlRE,
@@ -3474,7 +3474,7 @@ export function resolveLibCssFilename(
     return `${libOptions.fileName}.css`
   }
 
-  const packageJson = findNearestPackageData(root, packageCache)?.data
+  const packageJson = findNearestMainPackageData(root, packageCache)?.data
   const name = packageJson ? getPkgName(packageJson.name) : undefined
 
   if (!name)
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 0fb87c08328c7c..8abe4cd401fd3e 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -433,6 +433,8 @@ importers:
 
   packages/vite/src/node/__tests__/fixtures/test-dep-conditions: {}
 
+  packages/vite/src/node/__tests__/packages: {}
+
   packages/vite/src/node/__tests__/packages/child: {}
 
   packages/vite/src/node/__tests__/packages/module: {}