diff --git a/index.js b/index.js
index 0b1547f..b20c2d8 100644
--- a/index.js
+++ b/index.js
@@ -582,4 +582,6 @@ if (!MutationObserver) {
   MutationObserver = JsMutationObserver;
 }
 
-module.exports = MutationObserver;
+if (typeof module !== 'undefined') {
+  module.exports = MutationObserver;
+}