diff --git a/.changeset/slow-seahorses-grab.md b/.changeset/slow-seahorses-grab.md
new file mode 100644
index 00000000000..aa269d75978
--- /dev/null
+++ b/.changeset/slow-seahorses-grab.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/router-core': patch
+---
+
+prevent isServer exports from being transformed to top-level vars so rspack can dead-code eliminate them
diff --git a/packages/router-core/vite.config.ts b/packages/router-core/vite.config.ts
index 816b0602b87..413c56c4045 100644
--- a/packages/router-core/vite.config.ts
+++ b/packages/router-core/vite.config.ts
@@ -7,6 +7,13 @@ import type { ViteUserConfig } from 'vitest/config'
 
 const config = defineConfig({
   plugins: [minifyScriptPlugin()] as ViteUserConfig['plugins'],
+  build: {
+    rolldownOptions: {
+      output: {
+        topLevelVar: false,
+      },
+    },
+  },
   test: {
     name: packageJson.name,
     dir: './tests',