diff --git a/app/api/mobile/entities/course.rb b/app/api/mobile/entities/course.rb
index b9823d9ac..8e5609f32 100644
--- a/app/api/mobile/entities/course.rb
+++ b/app/api/mobile/entities/course.rb
@@ -3,10 +3,17 @@ module Mobile
     class Course < Grape::Entity
       def self.course_expose(field)
         expose field do |f,opt|
-          f[:course][field] || f[:course].__send__(field)
+          o = nil
+          o = f.img_url if f.respond_to?(:img_url)
+          if f.is_a? ::Course
+            o = f.send(field) if f.respond_to?(field)
+          else
+            f[:course][field] || f[:course].__send__(field)
+          end
+          o
         end
       end
-      expose :img_url
+      course_expose :img_url
       course_expose :attachmenttype
       course_expose :class_period
       course_expose :code