diff --git a/smash/web/models.py b/smash/web/models.py
index 0115708b05ce216bdc04e72f259f56ba201d2929..5388955992da548b95eb02e9787fd7621cebd2e1 100644
--- a/smash/web/models.py
+++ b/smash/web/models.py
@@ -116,6 +116,7 @@ class Subject(models.Model):
     )
     screening_number = models.CharField(max_length=50,
 	    blank=True,
+	    unique=True,
         verbose_name='Screening number'
     )
     nd_number = models.CharField(max_length=6,