diff --git a/lib/propmangle.js b/lib/propmangle.js
index ae2a3f44..b20a3815 100644
--- a/lib/propmangle.js
+++ b/lib/propmangle.js
@@ -44,6 +44,12 @@
 "use strict";
 
 function find_builtins() {
+
+    // Compatibility fix for es5.1 and earlier where Symbol isn't defined
+    if (!global.Symbol) {
+        global.Symbol = new Function();
+    }
+
     var a = [];
     [ Object, Array, Function, Number,
       String, Boolean, Error, Math,