diff --git a/core/mui/gtk_postbox.rb b/core/mui/gtk_postbox.rb
index 4097331..99b68a6 100644
--- a/core/mui/gtk_postbox.rb
+++ b/core/mui/gtk_postbox.rb
@@ -185,7 +185,7 @@ module Gtk
       @reply_widgets = []
       result = Gtk::HBox.new(false, 0).closeup(widget_tool).pack_start(widget_post).closeup(widget_remain).closeup(widget_send)
       w_replies = Gtk::VBox.new.add(result)
-      @to.select{|m|m.is_a?(Message)}.each{ |message|
+      @to.select{|m|m.is_a?(Diva::Model::MessageMixin) && m.respond_to?(:user) && m.user.is_a?(Diva::Model::UserMixin) }.each{ |message|
         w_reply = Gtk::HBox.new
         itv = Gtk::IntelligentTextview.new(message.to_show, 'font' => :mumble_basic_font)
         itv.style_generator = lambda{ get_backgroundstyle(message) }