diff --git a/app/models/attachment.rb b/app/models/attachment.rb
index 6e215e128..bb5a54dfc 100644
--- a/app/models/attachment.rb
+++ b/app/models/attachment.rb
@@ -686,7 +686,9 @@ class Attachment < ActiveRecord::Base
   #更新时间
   def update_others
     if self.course
-      self.course.update_course
+      if self.course.is_a?(::Course)
+        self.course.update_course
+      end
     end
   end
 end