diff --git a/lib/propmangle.js b/lib/propmangle.js
index 3923baa6..2089699c 100644
--- a/lib/propmangle.js
+++ b/lib/propmangle.js
@@ -66,7 +66,8 @@ function mangle_properties(ast, options) {
         cache : null,
         only_cache : false,
         regex : null,
-        ignore_quoted : false
+        ignore_quoted : false,
+        debug : false
     });
 
     var reserved = options.reserved;
@@ -83,6 +84,7 @@ function mangle_properties(ast, options) {
 
     var regex = options.regex;
     var ignore_quoted = options.ignore_quoted;
+    var debug = options.debug;
 
     var names_to_mangle = [];
     var unmangleable = [];
@@ -174,6 +176,9 @@ function mangle_properties(ast, options) {
         if (!should_mangle(name)) {
             return name;
         }
+        
+        if (debug)
+            return "_$" + name + "$_";
 
         var mangled = cache.props.get(name);
         if (!mangled) {