diff --git a/Gemfile b/Gemfile
index b482cb6fd..eef93c371 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,7 +3,11 @@ source 'https://ruby.taobao.org/'
 unless RUBY_PLATFORM =~ /w32/
   # unix-like only
   gem 'iconv'
-  gem "rmagick", "= 2.13.1" ## centos yum install ImageMagick-devel
+  if RUBY_PLATFORM =~ /darwin/
+    gem "rmagick", "= 2.15.4" ## osx must be this version
+  else
+    gem "rmagick", "= 2.13.1" ## centos yum install ImageMagick-devel
+  end
   gem 'certified'
 end
 
diff --git a/app/models/course.rb b/app/models/course.rb
index f286a2443..0c4acce97 100644
--- a/app/models/course.rb
+++ b/app/models/course.rb
@@ -470,8 +470,7 @@ class Course < ActiveRecord::Base
     if !code || code.size <5
       code = CODES.sample(5).join
       return generate_invite_code if Course.where(invite_code: code).present?
-      self[:invite_code] = code
-      save! && reload
+      update_attribute(:invite_code, code)
     end
     code
   end