diff --git a/lib/6to5/polyfill.js b/lib/6to5/polyfill.js
index 221aa97a57..12a9db8bb7 100644
--- a/lib/6to5/polyfill.js
+++ b/lib/6to5/polyfill.js
@@ -1,3 +1,6 @@
-require("es6-symbol/implement");
+if (typeof Symbol === "undefined") {
+  require("es6-symbol/implement");
+}
+
 require("es6-shim");
 require("regenerator/runtime");