diff --git a/packages/firestore/rollup.config.js b/packages/firestore/rollup.config.js
index e1aa90fe0e7..15fb5222c1f 100644
--- a/packages/firestore/rollup.config.js
+++ b/packages/firestore/rollup.config.js
@@ -51,6 +51,6 @@ export default [
     input: 'index.node.ts',
     output: [{ file: pkg.main, format: 'cjs' }],
     plugins,
-    external
+    external: [...external, 'util']
   }
 ];