diff --git a/packages/rolldown/src/node/rolldown/__tests__/build-runner.test.ts b/packages/rolldown/src/node/rolldown/__tests__/build-runner.test.ts
new file mode 100644
index 000000000..406fbe624
--- /dev/null
+++ b/packages/rolldown/src/node/rolldown/__tests__/build-runner.test.ts
@@ -0,0 +1,41 @@
+import type { ViteDevToolsNodeContext } from '@vitejs/devtools-kit'
+import { describe, expect, it, vi } from 'vitest'
+import { getBuildCommand, ROLLDOWN_DEVTOOLS_ENV, startBuild } from '../build-runner'
+
+function fakeContext() {
+  const startChildProcess = vi.fn(async (_exec: unknown, meta: { id: string }) => ({
+    ...meta,
+    status: 'running',
+    terminate: vi.fn(async () => {}),
+    getResult: vi.fn(),
+  }))
+  const context = {
+    cwd: '/project',
+    terminals: { sessions: new Map(), startChildProcess },
+  } as unknown as ViteDevToolsNodeContext
+  return { context, startChildProcess }
+}
+
+describe('rolldown build runner', () => {
+  it('builds for production even though the dev server runs with NODE_ENV=development', () => {
+    const { context } = fakeContext()
+    // The dev server sets `NODE_ENV=development`, and the spawned build
+    // inherits the dev server's env. Vite keeps an already-set `NODE_ENV`,
+    // so the build must override it to get a production bundle.
+    expect(getBuildCommand(context)).toEqual({
+      command: 'vite',
+      args: ['build'],
+      cwd: '/project',
+      env: { NODE_ENV: 'production', [ROLLDOWN_DEVTOOLS_ENV]: 'true' },
+    })
+  })
+
+  it('spawns the build with the production NODE_ENV', async () => {
+    const { context, startChildProcess } = fakeContext()
+    await startBuild(context)
+    expect(startChildProcess).toHaveBeenCalledTimes(1)
+    expect(startChildProcess.mock.calls[0]![0]).toMatchObject({
+      env: { NODE_ENV: 'production' },
+    })
+  })
+})
diff --git a/packages/rolldown/src/node/rolldown/build-runner.ts b/packages/rolldown/src/node/rolldown/build-runner.ts
index 3d4e18663..e4a6eba00 100644
--- a/packages/rolldown/src/node/rolldown/build-runner.ts
+++ b/packages/rolldown/src/node/rolldown/build-runner.ts
@@ -43,7 +43,14 @@ export function getBuildCommand(context: ViteDevToolsNodeContext): DevToolsChild
     command: 'vite',
     args: ['build'],
     cwd: context.cwd ?? process.cwd(),
-    env: { [ROLLDOWN_DEVTOOLS_ENV]: 'true' },
+    env: {
+      // The child inherits the dev server's env, where Vite has set
+      // `NODE_ENV=development`. `vite build` keeps an already-set `NODE_ENV`,
+      // which would keep every library's dev-only branches in the bundle, so
+      // pin what a plain `vite build` resolves to.
+      NODE_ENV: 'production',
+      [ROLLDOWN_DEVTOOLS_ENV]: 'true',
+    },
   }
 }