diff --git a/package.json b/package.json
index b53a809e..51799abf 100644
--- a/package.json
+++ b/package.json
@@ -4,6 +4,7 @@
   "description": "",
   "repository": "unjs/unenv",
   "license": "MIT",
+  "sideEffects": false,
   "exports": {
     ".": {
       "types": "./dist/index.d.ts",
@@ -51,4 +52,4 @@
     "unbuild": "^1.2.1"
   },
   "packageManager": "pnpm@8.6.12"
-}
\ No newline at end of file
+}
diff --git a/src/runtime/polyfill/package.json b/src/runtime/polyfill/package.json
new file mode 100644
index 00000000..3802144d
--- /dev/null
+++ b/src/runtime/polyfill/package.json
@@ -0,0 +1,3 @@
+{
+  "sideEffects": true
+}