diff --git a/lib/tasks/sync_ntnu_personal_data_tasks.rake b/lib/tasks/sync_ntnu_personal_data_tasks.rake
index 72b7254..12c6b08 100644
--- a/lib/tasks/sync_ntnu_personal_data_tasks.rake
+++ b/lib/tasks/sync_ntnu_personal_data_tasks.rake
@@ -128,7 +128,7 @@ def sync_conference_papers(query_result, user)
           wc.period_start_date = nil
         else
           wc.period_start_date = temp_date
-          wc.year = temp_date.year
+          wc.year = temp_date.year if wc.year.nil?
         end
       when '20101012151318602' # 會議結束日期
         wc.period_end_date = data['data'].first['v']