diff --git a/registrasion/controllers/cart.py b/registrasion/controllers/cart.py
index 204dc9f6..ff31bb95 100644
--- a/registrasion/controllers/cart.py
+++ b/registrasion/controllers/cart.py
@@ -132,6 +132,7 @@ class CartController(object):
 
         product_quantities = list(product_quantities)
 
+
         # n.b need to add have the existing items first so that the new
         # items override the old ones.
         all_product_quantities = dict(itertools.chain(
@@ -140,7 +141,16 @@ class CartController(object):
         )).items()
 
         # Validate that the limits we're adding are OK
-        self._test_limits(all_product_quantities)
+        products = set(product for product, q in product_quantities)
+        try:
+            self._test_limits(all_product_quantities)
+        except CartValidationError as ve:
+            # Only raise errors for products that we're explicitly
+            # Manipulating here.
+            for ve_field in ve.error_list:
+                product, message = ve_field.message
+                if product in products:
+                    raise ve
 
         new_items = []
         products = []
diff --git a/registrasion/tests/test_flag.py b/registrasion/tests/test_flag.py
index 3d8914a1..0b446c26 100644
--- a/registrasion/tests/test_flag.py
+++ b/registrasion/tests/test_flag.py
@@ -382,3 +382,15 @@ class FlagTestCases(RegistrationCartTestCase):
 
         with self.assertRaises(ValidationError):
             cart2.add_to_cart(self.PROD_1, 1)
+
+    def test_flag_failures_only_break_affected_products(self):
+        ''' If a flag fails, it should only affect its own products. '''
+
+        self.add_product_flag()
+        cart1 = TestingCartController.for_user(self.USER_1)
+        cart1.add_to_cart(self.PROD_2, 1)
+        cart1.add_to_cart(self.PROD_1, 1)
+        cart1.set_quantity(self.PROD_2, 0)
+
+        # The following should not fail, as PROD_3 is not affected by flag.
+        cart1.add_to_cart(self.PROD_3, 1)