diff --git a/finance/models.py b/finance/models.py
index f511f9c..89ad0ec 100755
--- a/finance/models.py
+++ b/finance/models.py
@@ -31,7 +31,7 @@ class Bill(models.Model):
         if self.invoice_set.exclude(status='F').exists():
             log = False
             try:
-                p = Progress.objects.get(user=user, course_token=self.course_token)
+                p = Progress.objects.get(user=user, course_token=str(self.course_token))
                 p.freeze = True
                 p.save()
             except Progress.DoesNotExist: