Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -35,31 +35,31 @@
  * Abstract base class for filters
  *
  * @param {string} text   string representation of the filter
  * @constructor
  */
 function Filter(text)
 {
   this.text = text;
-  this.subscriptions = [];
+  this.subscriptions = new Set();
 }
 exports.Filter = Filter;
 
 Filter.prototype =
 {
   /**
    * String representation of the filter
    * @type {string}
    */
   text: null,
 
   /**
    * Filter subscriptions the filter belongs to
-   * @type {Subscription[]}
+   * @type {Set.<Subscription>}
    */
   subscriptions: null,
 
   /**
    * Filter type as a string, e.g. "blocking".
    * @type {string}
    */
   get type()