diff --git a/lib/scope.js b/lib/scope.js
index b519ddbe..84c65759 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -552,21 +552,20 @@ AST_Toplevel.DEFMETHOD("compute_char_frequency", function(options) {
 });
 
 var nameGenerator = (function() {
-    var freq = Object.create(null);
     function init(chars) {
         var array = [];
         for (var i = 0; i < chars.length; i++) {
             var ch = chars[i];
             array.push(ch);
-            freq[ch] = -1e-2 * i;
+            frequency[ch] = -1e-2 * i;
         }
         return array;
     }
-    var trailing = init("0123456789");
-    var leading = init("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_");
-    var chars, frequency;
+    var chars, frequency, trailing, leading;
     function reset(options) {
-        frequency = Object.create(freq);
+        frequency = Object.create(null);
+        trailing = init(options.trailing_character_set);
+        leading = init(options.leading_character_set);
     }
     nameGenerator.consider = function(str, delta) {
         for (var i = str.length; --i >= 0;) {
@@ -581,13 +580,13 @@ var nameGenerator = (function() {
     };
     nameGenerator.reset = reset;
     function nameGenerator(num) {
-        var ret = "", base = 54;
+        var ret = "", base = leading.length;
         num++;
         do {
             num--;
             ret += chars[num % base];
             num = Math.floor(num / base);
-            base = 64;
+            base = leading.length + trailing.length;
         } while (num > 0);
         return ret;
     }