diff --git a/tos/models.py b/tos/models.py
index b40d052..3bf895b 100644
--- a/tos/models.py
+++ b/tos/models.py
@@ -1,6 +1,7 @@
 from django.contrib.auth.models import User 
 from django.core.exceptions import ValidationError 
 from django.db import models
+
 from django.utils.translation import ugettext_lazy as _ 
 
 class BaseModel(models.Model):
@@ -40,6 +41,10 @@ class TermsOfService(BaseModel):
 
         if self.active:
             TermsOfService.objects.exclude(id=self.id).update(active=False)
+            
+        else:
+            if not TermsOfService.objects.exclude(id=self.id).filter(active=True):
+                raise ValidationError('One of the terms of service must be marked active')
 
         super(TermsOfService,self).save(*args, **kwargs)
         
diff --git a/tos/tests/test_models.py b/tos/tests/test_models.py
index 22cc8be..a2e685b 100644
--- a/tos/tests/test_models.py
+++ b/tos/tests/test_models.py
@@ -1,4 +1,5 @@
 from django.contrib.auth.models import User 
+from django.core.exceptions import ValidationError 
 from django.test import TestCase 
 
 from tos.models import TermsOfService, UserAgreement, has_user_agreed_latest_tos
@@ -33,10 +34,19 @@ class TestModels(TestCase):
         first = TermsOfService.objects.get(id=self.tos1.id)
         self.assertFalse(first.active)
         
+        # latest is active though
+        self.assertTrue(latest.active)        
+        
     def test_terms_of_service_manager(self):
         
         self.assertEquals(TermsOfService.objects.get_current_tos(), self.tos1)
         
+    def test_validation_error_all_set_false(self):
+        """ If you try and set all to false the model will throw a ValidationError """
+        
+        self.tos1.active=False
+        self.assertRaises(ValidationError, self.tos1.save)        
+        
     def test_user_agreement(self):
         
         # simple agreement