diff --git a/sbas/templates/sbas/exam_start.html b/sbas/templates/sbas/exam_start.html
index b6f5b803..e845e025 100755
--- a/sbas/templates/sbas/exam_start.html
+++ b/sbas/templates/sbas/exam_start.html
@@ -4,6 +4,7 @@
 
 <h2>{{exam.name}}</h2>
 
+Enter your CID in the below box.
 <input id="cid-box" type="text" value="Candidate ID">
  
 <button>Start exam</button>
@@ -12,7 +13,12 @@
     $(document).ready(function () {
         $("button").click(() => {
         let cid = $("#cid-box").val();
+
+        if (Number.isInteger(cid)) {
         window.location.replace("{% url 'sbas:exam_take' pk=exam.pk sk=0 cid='0000000' %}".replace("0000000", cid));
+        } else {
+            alert("Please enter a valid Candidate ID (CID).")
+        }
         });
     });
 </script>