diff --git a/anatomy/models.py b/anatomy/models.py
index 34d5620c..8b14ca2e 100644
--- a/anatomy/models.py
+++ b/anatomy/models.py
@@ -331,7 +331,7 @@ class CidUserAnswer(models.Model):
     )
     answer = models.TextField(max_length=500, blank=True)
 
-    cid = models.IntegerField(blank=True, null=True)
+    cid = models.BigIntegerField(blank=True, null=True, help_text="Candidate ID (limitied by BigIntegerField size)")
 
     # Each user answer is associated with a particular exam
     exam = models.ForeignKey(