diff --git a/judge/forms.py b/judge/forms.py
index 5bc43a9..32fc75e 100644
--- a/judge/forms.py
+++ b/judge/forms.py
@@ -538,9 +538,37 @@ class ContestProblemForm(ModelForm):
         }
 
 
+class ContestProblemModelFormSet(BaseModelFormSet):
+    def is_valid(self):
+        valid = super().is_valid()
+
+        if not valid:
+            return valid
+
+        problems = set()
+        duplicates = []
+
+        for form in self.forms:
+            if form.cleaned_data and not form.cleaned_data.get("DELETE", False):
+                problem = form.cleaned_data.get("problem")
+                if problem in problems:
+                    duplicates.append(problem)
+                else:
+                    problems.add(problem)
+
+        if duplicates:
+            for form in self.forms:
+                problem = form.cleaned_data.get("problem")
+                if problem in duplicates:
+                    form.add_error("problem", _("This problem is duplicated."))
+            return False
+
+        return True
+
+
 class ContestProblemFormSet(
     formset_factory(
-        ContestProblemForm, formset=BaseModelFormSet, extra=6, can_delete=True
+        ContestProblemForm, formset=ContestProblemModelFormSet, extra=6, can_delete=True
     )
 ):
     model = ContestProblem
diff --git a/judge/views/organization.py b/judge/views/organization.py
index 962be71..0576afe 100644
--- a/judge/views/organization.py
+++ b/judge/views/organization.py
@@ -926,8 +926,12 @@ class EditOrganizationContest(
             super().post(request, *args, **kwargs)
             return HttpResponseRedirect(
                 reverse(
-                    "organization_contests",
-                    args=(self.organization_id, self.organization.slug),
+                    "organization_contest_edit",
+                    args=(
+                        self.organization_id,
+                        self.organization.slug,
+                        self.contest.key,
+                    ),
                 )
             )
 
diff --git a/locale/vi/LC_MESSAGES/django.po b/locale/vi/LC_MESSAGES/django.po
index d1e8a78..0cb9282 100644
--- a/locale/vi/LC_MESSAGES/django.po
+++ b/locale/vi/LC_MESSAGES/django.po
@@ -2,7 +2,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: lqdoj2\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2023-08-26 03:42+0700\n"
+"POT-Creation-Date: 2023-08-26 05:31+0700\n"
 "PO-Revision-Date: 2021-07-20 03:44\n"
 "Last-Translator: Icyene\n"
 "Language-Team: Vietnamese\n"
@@ -555,6 +555,10 @@ msgstr ""
 msgid "You don't have permission in this group."
 msgstr "Bạn không có quyền chấm lại bài."
 
+#: judge/forms.py:563
+msgid "This problem is duplicated."
+msgstr "Bài này bị lặp"
+
 #: judge/jinja2/datetime.py:26 templates/blog/blog.html:28
 #: templates/blog/dashboard.html:21
 msgid "N j, Y, g:i a"
@@ -2883,19 +2887,19 @@ msgstr "Thay đổi Email"
 msgid "Change Email"
 msgstr "Thay đổi Email"
 
-#: judge/views/email.py:65 templates/user/edit-profile.html:120
+#: judge/views/email.py:71 templates/user/edit-profile.html:120
 msgid "Change email"
 msgstr "Thay đổi email"
 
-#: judge/views/email.py:89
+#: judge/views/email.py:94
 msgid "Success"
 msgstr "Thành công"
 
-#: judge/views/email.py:93
+#: judge/views/email.py:98
 msgid "Invalid"
 msgstr "Không hợp lệ"
 
-#: judge/views/email.py:102
+#: judge/views/email.py:107
 msgid "Email change pending"
 msgstr "Yêu cầu thay đổi email đang đợi xác thực."
 
@@ -4426,8 +4430,8 @@ msgstr "Hoạt động"
 
 #: templates/organization/blog/edit.html:36
 #: templates/organization/contest/add.html:36
-#: templates/organization/contest/edit.html:87
-#: templates/organization/form.html:24
+#: templates/organization/contest/edit.html:86
+#: templates/organization/form.html:23
 msgid "Save"
 msgstr "Lưu"
 
@@ -4441,12 +4445,15 @@ msgid "Author"
 msgstr "Tác giả"
 
 #: templates/organization/blog/pending.html:14
-#, fuzzy
-#| msgid "posted time"
 msgid "Post time"
-msgstr "thời gian đăng"
+msgstr "Thời gian đăng"
 
-#: templates/organization/contest/edit.html:61
+#: templates/organization/contest/edit.html:40
+#: templates/organization/form.html:6
+msgid "Please fix below errors"
+msgstr "Vui lòng sửa các lỗi bên dưới"
+
+#: templates/organization/contest/edit.html:60
 msgid "If you run out of rows, click Save"
 msgstr "Ấn nút lưu lại nếu cần thêm hàng"
 
diff --git a/resources/widgets.scss b/resources/widgets.scss
index f33882d..085d508 100644
--- a/resources/widgets.scss
+++ b/resources/widgets.scss
@@ -606,6 +606,14 @@ ul.select2-selection__rendered {
     background: gray;
 }
 
+ul.errorlist {
+    margin: 0px;
+    text-align: right;
+    list-style: none;
+    padding: 0px;
+    color: red;
+}
+
 .registration-form {
     .sortedm2m-container, .sortedm2m-container p.selector-filter {
         width: 300px;
@@ -682,12 +690,6 @@ ul.select2-selection__rendered {
         width: 450px;
     }
 
-    ul.errorlist {
-        margin: 0px;
-        text-align: right;
-        list-style: none;
-    }
-
     .full-textfield {
         padding-top: 0.5em;
     }
diff --git a/templates/organization/contest/edit.html b/templates/organization/contest/edit.html
index 101bfbf..5682504 100644
--- a/templates/organization/contest/edit.html
+++ b/templates/organization/contest/edit.html
@@ -34,11 +34,10 @@
 {% block middle_content %}
   <form action="" method="post">
     {% csrf_token %}
-    {% if form.errors %}
+    {% if form.errors or problems_form.errors %}
       <div class="alert alert-danger alert-dismissable">
         <a href="#" class="close">x</a>
-        {{ form.non_field_errors() }}
-        {{ form.errors }}
+        {{_("Please fix below errors")}}
       </div>
     {% endif %}
     {% for field in form %}
diff --git a/templates/organization/form.html b/templates/organization/form.html
index 5201ace..85c86d9 100644
--- a/templates/organization/form.html
+++ b/templates/organization/form.html
@@ -3,8 +3,7 @@
   {% if form.errors %}
     <div class="alert alert-danger alert-dismissable">
       <a href="#" class="close">x</a>
-      {{ form.non_field_errors() }}
-      {{ form.errors }}
+      {{ _("Please fix below errors") }}
     </div>
   {% endif %}
   {% for field in form %}