diff --git a/lib/propmangle.js b/lib/propmangle.js
index 3c75cac9..927d1e8e 100644
--- a/lib/propmangle.js
+++ b/lib/propmangle.js
@@ -84,6 +84,7 @@ function mangle_properties(ast, options) {
 
     var regex = options.regex;
     var ignore_quoted = options.ignore_quoted;
+    var debug = options.debug;
 
     // note debug is either false (disabled), or a string of the debug suffix to use (enabled).
     // note debug may be enabled as an empty string, which is falsey. Also treat passing 'true'
@@ -185,6 +186,9 @@ function mangle_properties(ast, options) {
         if (!should_mangle(name)) {
             return name;
         }
+        
+        if (debug)
+            return "_$" + name + "$_";
 
         var mangled = cache.props.get(name);
         if (!mangled) {