diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 43a893097..a7c015210 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.13.50",
+    "version": "2.13.51",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
diff --git a/packages/hydrooj/src/entry/master.ts b/packages/hydrooj/src/entry/master.ts
index c6fb595f4..41132e17c 100644
--- a/packages/hydrooj/src/entry/master.ts
+++ b/packages/hydrooj/src/entry/master.ts
@@ -59,7 +59,7 @@ export async function load(call: Entry) {
     for (const i of builtinModel) require(`../model/${i}`);
     const modelSystem = require('../model/system');
     const scripts = require('../upgrade');
-    let dbVer = (await modelSystem.get('db.ver')) || 0;
+    let dbVer = (await modelSystem.get('db.ver')) ?? 0;
     const expected = scripts.length;
     while (dbVer < expected) {
         logger.info('Upgrading database: from %d to %d', dbVer, expected);
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index 6940997ae..134d8080d 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -241,7 +241,7 @@ class ContestProblemHandler extends ContestHandler {
         ]);
         this.attended = this.tsdoc && this.tsdoc.attend === 1;
         this.response.template = 'problem_detail.html';
-        if (contest.isDone(this.tdoc)) {
+        if (!contest.isDone(this.tdoc)) {
             if (!this.attended) throw new ContestNotAttendedError(this.tdoc.docId);
             if (contest.isNotStarted(this.tdoc)) throw new ContestNotLiveError(this.tdoc.docId);
         }
@@ -272,6 +272,7 @@ class ContestProblemSubmitHandler extends ContestProblemHandler {
     @param('tid', Types.ObjectID)
     @param('pid', Types.UnsignedInt)
     async prepare(domainId: string, tid: ObjectID, pid: number) {
+        if (contest.isOngoing(this.tdoc)) throw new ContestNotLiveError(this.tdoc.docId);
         let rdocs = [];
         if (this.canShowRecord(this.tdoc)) {
             rdocs = await record.getUserInProblemMulti(
diff --git a/packages/hydrooj/src/model/setting.ts b/packages/hydrooj/src/model/setting.ts
index 05daae503..0cf40c9ee 100644
--- a/packages/hydrooj/src/model/setting.ts
+++ b/packages/hydrooj/src/model/setting.ts
@@ -138,7 +138,7 @@ SystemSetting(
     Setting('setting_session', 'session.secure', null, false, 'boolean', 'session.secure'),
     Setting('setting_session', 'session.saved_expire_seconds', null, 3600 * 24 * 30, 'number', 'Saved session expire seconds'),
     Setting('setting_session', 'session.unsaved_expire_seconds', null, 3600 * 3, 'number', 'Unsaved session expire seconds'),
-    Setting('setting_storage', 'db.ver', null, 1, 'number', 'Database version', null, FLAG_DISABLED | FLAG_HIDDEN),
+    Setting('setting_storage', 'db.ver', null, 0, 'number', 'Database version', null, FLAG_DISABLED | FLAG_HIDDEN),
     Setting('setting_storage', 'user', null, 1, 'number', 'User Counter', null, FLAG_DISABLED | FLAG_HIDDEN),
 );