diff --git a/contest/models.py b/contest/models.py
index 7e672041..e9e95564 100644
--- a/contest/models.py
+++ b/contest/models.py
@@ -125,8 +125,8 @@ class ContestRank(models.Model):
             raise ValueError("Error submission type")
 
         # 这道题以前提交过
-        if submission.problem_id in self.submission_info:
-            info = self.submission_info[submission.problem_id]
+        if str(submission.problem_id) in self.submission_info:
+            info = self.submission_info[str(submission.problem_id)]
             # 如果这道题目已经 ac 了就跳过
             if info["is_ac"]:
                 return
@@ -167,5 +167,5 @@ class ContestRank(models.Model):
             else:
                 info["is_ac"] = False
                 info["error_number"] = 1
-        self.submission_info[submission.problem_id] = info
+        self.submission_info[str(submission.problem_id)] = info
         self.save()