Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -621,22 +621,31 @@
 RegExpFilter.prototype = extend(ActiveFilter, {
   /**
    * @see ActiveFilter.domainSourceIsLowerCase
    */
   domainSourceIsLowerCase: true,
 
   /**
    * Number of filters contained, will always be 1 (required to
-   * optimize Matcher).
+   * optimize {@link Matcher}).
    * @type {number}
    */
   length: 1,
 
   /**
+   * The filter itself (required to optimize {@link Matcher}).
+   * @type {RegExpFilter}
+   */
+  get 0()
+  {
+    return this;
+  },
+
+  /**
    * @see ActiveFilter.domainSeparator
    */
   domainSeparator: "|",
 
   /**
    * Expression from which a regular expression should be generated -
    * for delayed creation of the regexp property
    * @type {string}
@@ -715,21 +724,16 @@
         this.isActiveOnDomain(docDomain, sitekey) && this.regexp.test(location))
     {
       return true;
     }
     return false;
   }
 });
 
-// Required to optimize Matcher, see also RegExpFilter.prototype.length
-Object.defineProperty(RegExpFilter.prototype, "0", {
-  get() { return this; }
-});
-
 /**
  * Creates a RegExp filter from its text representation
  * @param {string} text   same as in Filter()
  * @return {Filter}
  */
 RegExpFilter.fromText = function(text)
 {
   let blocking = true;