diff --git a/registrasion/controllers/cart.py b/registrasion/controllers/cart.py
index aec77c07..f3bcabf1 100644
--- a/registrasion/controllers/cart.py
+++ b/registrasion/controllers/cart.py
@@ -1,14 +1,16 @@
+import collections
 import datetime
 import discount
 
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError
 from django.db import transaction
-from django.db.models import Max
+from django.db.models import Max, Sum
 from django.utils import timezone
 
 from registrasion import models as rego
 
+from category import CategoryController
 from conditions import ConditionController
 from product import ProductController
 
@@ -71,12 +73,40 @@ class CartController(object):
     @transaction.atomic
     def set_quantities(self, product_quantities):
 
+        items_in_cart = rego.ProductItem.objects.filter(cart=self.cart)
+
         # Remove all items that we're updating
-        rego.ProductItem.objects.filter(
-            cart=self.cart,
+        items_in_cart.filter(
             product__in=(i[0] for i in product_quantities),
         ).delete()
 
+        # Collect by category
+        by_cat = collections.defaultdict(list)
+        for product, quantity in product_quantities:
+            by_cat[product.category].append((product, quantity))
+
+        # Test each category limit here
+        for cat in by_cat:
+            ctrl = CategoryController(cat)
+            limit = ctrl.user_quantity_remaining(self.cart.user)
+
+            # Get the amount so far in the cart
+            cat_items = items_in_cart.filter(product__category=cat)
+            so_far = cat_items.aggregate(Sum("quantity"))["quantity__sum"] or 0
+            to_add = sum(i[1] for i in by_cat[cat])
+
+            if so_far + to_add > limit:
+                # TODO: batch errors
+                raise ValidationError(
+                    "You may only have %d items in category: %s" % (
+                        limit, cat.name,
+                    )
+                )
+
+        # Test each product limit here
+
+        # Test each enabling condition here
+
         for product, quantity in product_quantities:
             self._set_quantity_old(product, quantity)
 
@@ -86,7 +116,7 @@ class CartController(object):
         ''' Sets the _quantity_ of the given _product_ in the cart to the given
         _quantity_. '''
 
-        self.set_quantities( ((product,quantity),) )
+        self.set_quantities(((product, quantity),))
 
     def _set_quantity_old(self, product, quantity):
         ''' Sets the _quantity_ of the given _product_ in the cart to the given
diff --git a/registrasion/controllers/category.py b/registrasion/controllers/category.py
index 5a6b4a68..7f244263 100644
--- a/registrasion/controllers/category.py
+++ b/registrasion/controllers/category.py
@@ -1,7 +1,7 @@
-from .product import ProductController
-
 from registrasion import models as rego
 
+from django.db.models import Sum
+
 
 class AllProducts(object):
     pass
@@ -9,12 +9,18 @@ class AllProducts(object):
 
 class CategoryController(object):
 
+    def __init__(self, category):
+        self.category = category
+
     @classmethod
     def available_categories(cls, user, products=AllProducts):
         ''' Returns the categories available to the user. Specify `products` if
         you want to restrict to just the categories that hold the specified
         products, otherwise it'll do all. '''
 
+        # STOPGAP -- this needs to be elsewhere tbqh
+        from product import ProductController
+
         if products is AllProducts:
             products = rego.Product.objects.all()
 
@@ -24,3 +30,33 @@ class CategoryController(object):
         )
 
         return set(i.category for i in available)
+
+    def user_quantity_remaining(self, user):
+        ''' Returns the number of items from this category that the user may
+        add in the current cart. '''
+
+        cat_limit = self.category.limit_per_user
+
+        if cat_limit is None:
+            # We don't need to waste the following queries
+            return 99999999
+
+        carts = rego.Cart.objects.filter(
+            user=user,
+            active=False,
+            released=False,
+        )
+
+        items = rego.ProductItem.objects.filter(
+            cart__in=carts,
+            product__category=self.category,
+        )
+
+        cat_count = items.aggregate(Sum("quantity"))["quantity__sum"] or 0
+        
+        cat_limit = self.category.limit_per_user
+
+        if cat_limit is None:
+            return 999999  # We should probably work on this.
+        else:
+            return cat_limit - cat_count
diff --git a/registrasion/controllers/product.py b/registrasion/controllers/product.py
index abb5947d..f92ecb10 100644
--- a/registrasion/controllers/product.py
+++ b/registrasion/controllers/product.py
@@ -4,6 +4,7 @@ from django.db.models import Q
 from django.db.models import Sum
 from registrasion import models as rego
 
+from category import CategoryController
 from conditions import ConditionController
 
 
@@ -32,6 +33,7 @@ class ProductController(object):
         out = [
             product
             for product in all_products
+            if CategoryController(product.category).user_quantity_remaining(user) > 0
             if cls(product).user_can_add_within_limit(user, 1, past_carts=True)
             if cls(product).can_add_with_enabling_conditions(user, 0)
         ]
@@ -54,23 +56,14 @@ class ProductController(object):
         )
 
         prod_items = items.filter(product=self.product)
-        cat_items = items.filter(product__category=self.product.category)
 
         prod_count = prod_items.aggregate(Sum("quantity"))["quantity__sum"]
-        cat_count = cat_items.aggregate(Sum("quantity"))["quantity__sum"]
-
-        if prod_count is None:
-            prod_count = 0
-        if cat_count is None:
-            cat_count = 0
+        prod_count = prod_count or 0
 
         prod_limit = self.product.limit_per_user
         prod_met = prod_limit is None or quantity + prod_count <= prod_limit
 
-        cat_limit = self.product.category.limit_per_user
-        cat_met = cat_limit is None or quantity + cat_count <= cat_limit
-
-        if prod_met and cat_met:
+        if prod_met:
             return True
         else:
             return False