diff --git a/ogcp/templates/actions/session.html b/ogcp/templates/actions/session.html
index 151c6aa..421226d 100644
--- a/ogcp/templates/actions/session.html
+++ b/ogcp/templates/actions/session.html
@@ -36,7 +36,7 @@ The selected clients have different installed OS:
                 {% for os_choice in form.os %}
                     <tr data-toggle="fieldset-entry">
                         <td class="radio-container">
-                            {{ os_choice(class_="form-control") }}
+                            {{ os_choice(class_="form-control", required=True) }}
                             <b>{{ os_choice.label.text }}</b>
                         </td>
                         <td>