diff --git a/db/migrate/20190626070641_add_limit_for_shixuns.rb b/db/migrate/20190626070641_add_limit_for_shixuns.rb
index 1de29c80..e403c061 100644
--- a/db/migrate/20190626070641_add_limit_for_shixuns.rb
+++ b/db/migrate/20190626070641_add_limit_for_shixuns.rb
@@ -1,5 +1,8 @@
 class AddLimitForShixuns < ActiveRecord::Migration
   def up
+    if !Challenge.first.has_attribute?(:exec_time)
+      add_column :challenges, :exec_time, :integer, :default => 120
+    end
     Shixun.find_each do |shixun|
       shixun.challenges.update_all(:exec_time => shixun.exec_time)
       shixun.mirror_repositories.each do |mirror|