diff --git a/package.json b/package.json
index e8ea008..32fb077 100644
--- a/package.json
+++ b/package.json
@@ -21,6 +21,7 @@
         "type": "git",
         "url": "https://github.com/Microsoft/tslib.git"
     },
+    "sideEffects": false,
     "main": "tslib.js",
     "module": "tslib.es6.js",
     "jsnext:main": "tslib.es6.js",