diff --git a/lib/tasks/competition_extra_course_statistic.rake b/lib/tasks/competition_extra_course_statistic.rake
index 924ca959e..724e53ca2 100644
--- a/lib/tasks/competition_extra_course_statistic.rake
+++ b/lib/tasks/competition_extra_course_statistic.rake
@@ -56,7 +56,7 @@ namespace :competition do
       forked_shixun_map = Shixun.where(status: 2, fork_from: shixun_ids).select('id, fork_from')
       forked_shixun_map = forked_shixun_map.each_with_object({}) { |sx, obj| obj[sx.id] = sx.fork_from }
       forked_myshixun_count_map = get_valid_myshixun_count(forked_shixun_map.keys)
-      forked_myshixun_count_map.each { |k, v| myshixun_count_map[forked_shixun_map[k]] += v }
+      forked_myshixun_count_map.each { |k, v| myshixun_count_map[forked_shixun_map[k]].to_i += v.to_i }
 
       course_count_map = get_valid_course_count(shixun_ids, end_time)
       forked_map = get_valid_course_count(forked_shixun_map.keys, end_time)