diff --git a/ctfpad/forms.py b/ctfpad/forms.py
index 165bbdc..881c505 100644
--- a/ctfpad/forms.py
+++ b/ctfpad/forms.py
@@ -126,14 +126,21 @@ class Meta:
             "tags",
         ]
 
-    is_update = True
-
     def cleaned_tags(self):
         data = [x.lower() for x in self.cleaned_data['tags'].split()]
         return data
 
+    def clean_flag(self):
+        flag = self.cleaned_data.get("flag")
+        prefix = self.instance.ctf.flag_prefix
+
+        if flag and prefix and not flag.startswith(prefix):
+            self.add_error("flag", f"Unexpected format for flag (missing '{prefix}')")
+
+        return flag
+
 
-class ChallengeSetFlagForm(forms.ModelForm):
+class ChallengeSetFlagForm(ChallengeUpdateForm):
     class Meta:
         model = Challenge
         fields = [
diff --git a/ctfpad/templates/ctfpad/challenges/create.html b/ctfpad/templates/ctfpad/challenges/create.html
index 9cf0949..d24d4d7 100644
--- a/ctfpad/templates/ctfpad/challenges/create.html
+++ b/ctfpad/templates/ctfpad/challenges/create.html
@@ -80,7 +80,7 @@ <h5 class="card-title">
                         <textarea id="{{form.description.id_for_label}}" name="{{form.description.html_name }}" placeholder="{{form.description.label}}" value="{{form.description.value}}" class="form-control">{% if form.description %}{{form.description.value}}{%endif%}</textarea>
                     </div>
 
-                    {% if form.is_update %}
+                    {% if form.instance.creation_time %}
                     <label class="label"><strong>Flag</strong></label>
                     <div class="input-group mb-3">
                         <div class="input-group-append">
@@ -108,7 +108,7 @@ <h5 class="card-title">
                     {% endif %}
                     {% endif %}
 
-                    {% if form.is_update %}
+                    {% if form.instance.creation_time %}
                     <label class="label"><strong>HedgeDoc ID </strong></label>
                     <div class="input-group mb-3">
                         <div class="input-group-append">
@@ -138,7 +138,7 @@ <h5 class="card-title">
 
                 <div class="card-footer text-muted">
                     <div class="control card-footer-item">
-                        {% if form.is_update %}
+                        {% if form.instance.creation_time %}
                         <button type="button" class="btn-primary btn-sm btn-block" onclick="this.form.submit();">Update Challenge</button>
                         {% else %}
                         <button type="button" class="btn-primary btn-sm btn-block" onclick="this.form.submit();">Create Challenge</button>
diff --git a/ctfpad/templates/ctfpad/challenges/detail.html b/ctfpad/templates/ctfpad/challenges/detail.html
index 195d5a6..5d10db8 100644
--- a/ctfpad/templates/ctfpad/challenges/detail.html
+++ b/ctfpad/templates/ctfpad/challenges/detail.html
@@ -53,7 +53,7 @@
 
 <div class="row">
     <div class="col-md-3" id="challenge_info_left_menu">
-
+        {{ form.errors }}
 		<div class="card card-body">
 			<a class="btn btn-warning btn-sm btn-block" href="{% url 'ctfpad:challenges-edit' challenge.id %}"><strong>Edit Challenge</strong></a>
             <ul class="list-group">
diff --git a/ctfpad/views/challenges.py b/ctfpad/views/challenges.py
index 012eb69..59dabb8 100644
--- a/ctfpad/views/challenges.py
+++ b/ctfpad/views/challenges.py
@@ -88,6 +88,7 @@ def get_success_url(self):
 
 class ChallengeSetFlagView(ChallengeUpdateView):
     form_class = ChallengeSetFlagForm
+    template_name = "ctfpad/challenges/detail.html"
 
     def get_success_url(self):
         return reverse("ctfpad:challenges-detail", kwargs={'pk': self.object.pk})
@@ -97,9 +98,6 @@ def form_valid(self, form):
             messages.error(self.request, f"Cannot score when CTF is over")
             return redirect("ctfpad:challenges-detail", self.object.id)
 
-        if not form.instance.flag.startswith( form.instance.ctf.flag_prefix ):
-            messages.warning(self.request, f"Unexpected format for flag (missing '{form.instance.ctf.flag_prefix}')")
-
         return super().form_valid(form)