diff --git a/app/routes.py b/app/routes.py
index 90248f5..407c388 100644
--- a/app/routes.py
+++ b/app/routes.py
@@ -27,6 +27,9 @@ def index():
 def Semestre(num):
     form = SemestreForm()
     semestre = models.Semestre.query.filter_by(num=num).first()
+    if semestre == None:
+        flash("Ce Semestre n'existe pas!", "error")
+        return redirect(url_for("index"))
     for i, ue in enumerate(semestre.ues):
         if form.ueform.__len__() < len(semestre.ues): form.ueform.append_entry(data={"ue": ue.code})
         # Donne aux dropdowns la liste des objets de formations que les ACs possèdent sans doublons
diff --git a/app/templates/base.html b/app/templates/base.html
index 554bbb0..d88b109 100644
--- a/app/templates/base.html
+++ b/app/templates/base.html
@@ -96,12 +96,27 @@
     <!-- Contenu de la page -->
     <div class="container">
         <div class="box">
-            {% with messages = get_flashed_messages() %}
-            {% if messages %}
-            <script>
-                alert("{% for message in messages %}{{message}}{% endfor %}");
-            </script>
-            {% endif %}
+            {% with messages = get_flashed_messages(category_filter=["error"]) %}
+                {% if messages %}
+                <article class="message is-danger">
+                    <div class="message-body">
+                        {% for message in messages %}
+                        <p>{{message}}</p>
+                        {% endfor %}
+                    </div>
+                </article>     
+                {% endif %}
+            {% endwith %}
+            {% with messages = get_flashed_messages(category_filter=["success"]) %}
+                {% if messages %}
+                <article class="message is-success">
+                    <div class="message-body">
+                        {% for message in messages %}
+                        <p>{{message}}</p>
+                        {% endfor %}
+                    </div>
+                </article>     
+                {% endif %}
             {% endwith %}
             {% block content %}
             {% endblock %}