diff --git a/js/ui/messageTray.js b/js/ui/messageTray.js
index dcba4788ffeb6b356bd033b2bee676790331e7e3..8f81304510adfd741e39e18caf49ad0b30af6cb4 100644
--- a/js/ui/messageTray.js
+++ b/js/ui/messageTray.js
@@ -708,6 +708,12 @@ var Source = class Source {
         return this._policy;
     }
 
+    set policy(policy) {
+        if (this._policy)
+            this._policy.destroy();
+        this._policy = policy;
+    }
+
     get count() {
         return this.notifications.length;
     }