diff --git a/lib/hoptoad_notifier/notice.rb b/lib/hoptoad_notifier/notice.rb
index a08b220..5c571d7 100644
--- a/lib/hoptoad_notifier/notice.rb
+++ b/lib/hoptoad_notifier/notice.rb
@@ -326,7 +326,8 @@ def rack_session
 
     def also_use_rack_params_filters
       if args[:rack_env]
-        self.params_filters += rack_request.env["action_dispatch.parameter_filter"] || []
+        @params_filters ||= []
+        @params_filters += rack_request.env["action_dispatch.parameter_filter"] || []
       end
     end