diff --git a/modules/contest.js b/modules/contest.js
index 303de97..dbc8151 100644
--- a/modules/contest.js
+++ b/modules/contest.js
@@ -83,7 +83,11 @@ app.post('/contest/:id/edit', async (req, res) => {
       ranklist = contest.ranklist;
     }
 
-    ranklist.ranking_params = JSON.parse(req.body.ranking_params);
+    try {
+      ranklist.ranking_params = JSON.parse(req.body.ranking_params);
+    } catch (e) {
+      ranklist.ranking_params = {};
+    }
     await ranklist.save();
     contest.ranklist_id = ranklist.id;
 
diff --git a/views/contest_edit.ejs b/views/contest_edit.ejs
index 7a09d68..f0ba65a 100644
--- a/views/contest_edit.ejs
+++ b/views/contest_edit.ejs
@@ -48,7 +48,7 @@
               </div>
             </div>
             <div class="field">
-                <label>排行参数</label>
+                <label>排行参数（格式：<code>{ "题目 ID": 分值倍数 }</code>）</label>
                 <input type="text" name="ranking_params" value="<%= contest.ranklist ? JSON.stringify(contest.ranklist.ranking_params) : '' %>">
             </div>
             <div class="field">