diff --git a/lms/djangoapps/shoppingcart/models.py b/lms/djangoapps/shoppingcart/models.py
index e2dad911da..895f466273 100644
--- a/lms/djangoapps/shoppingcart/models.py
+++ b/lms/djangoapps/shoppingcart/models.py
@@ -158,8 +158,7 @@ class PaidCourseRegistration(OrderItem):
         Is the course defined by course_id in the order?
         """
         return course_id in [item.paidcourseregistration.course_id
-                             for item in order.orderitem_set.all()
-                             if item.is_of_subtype(PaidCourseRegistration)]
+                             for item in order.orderitem_set.all().select_subclasses("paidcourseregistration")]
 
     @classmethod
     def add_to_order(cls, order, course_id, mode_slug=CourseMode.DEFAULT_MODE_SLUG, cost=None, currency=None):
@@ -169,15 +168,11 @@ class PaidCourseRegistration(OrderItem):
 
         Returns the order item
         """
-        super(PaidCourseRegistration, cls).add_to_order(order, course_id, cost, currency=currency)
-
         # TODO: Possibly add checking for whether student is already enrolled in course
         course = course_from_id(course_id)  # actually fetch the course to make sure it exists, use this to
                                             # throw errors if it doesn't
-        item, created = cls.objects.get_or_create(order=order, user=order.user, course_id=course_id)
-        item.status = order.status
 
-        ### Get this course_mode
+        ### handle default arguments for mode_slug, cost, currency
         course_mode = CourseMode.mode_for_course(course_id, mode_slug)
         if not course_mode:
             # user could have specified a mode that's not set, in that case return the DEFAULT_MODE
@@ -187,6 +182,11 @@ class PaidCourseRegistration(OrderItem):
         if not currency:
             currency = course_mode.currency
 
+        super(PaidCourseRegistration, cls).add_to_order(order, course_id, cost, currency=currency)
+
+        item, created = cls.objects.get_or_create(order=order, user=order.user, course_id=course_id)
+        item.status = order.status
+
         item.mode = course_mode.slug
         item.qty = 1
         item.unit_cost = cost
diff --git a/lms/djangoapps/shoppingcart/processors/CyberSource.py b/lms/djangoapps/shoppingcart/processors/CyberSource.py
index d8e53843cc..e7f593db4a 100644
--- a/lms/djangoapps/shoppingcart/processors/CyberSource.py
+++ b/lms/djangoapps/shoppingcart/processors/CyberSource.py
@@ -24,7 +24,7 @@ orderPage_version = settings.CC_PROCESSOR['CyberSource'].get('ORDERPAGE_VERSION'
 purchase_endpoint = settings.CC_PROCESSOR['CyberSource'].get('PURCHASE_ENDPOINT','')
 payment_support_email = settings.PAYMENT_SUPPORT_EMAIL
 
-def process_postpay_callback(request):
+def process_postpay_callback(params):
     """
     The top level call to this module, basically
     This function is handed the callback request after the customer has entered the CC info and clicked "buy"
@@ -36,7 +36,6 @@ def process_postpay_callback(request):
     If unsuccessful this function should not have those side effects but should try to figure out why and
     return a helpful-enough error message in error_html.
     """
-    params = request.POST.dict()
     try:
         verify_signatures(params)
         result = payment_accepted(params)
@@ -164,17 +163,18 @@ def payment_accepted(params):
 
     if valid_params['decision'] == 'ACCEPT':
         try:
-            # Moved reading of charged_amount from the valid_params loop above because
+            # Moved reading of charged_amount here from the valid_params loop above because
             # only 'ACCEPT' messages have a 'ccAuthReply_amount' parameter
             charged_amt = Decimal(params['ccAuthReply_amount'])
         except InvalidOperation:
             raise CCProcessorDataException(
-                _("The payment processor returned a badly-typed value {0} for param {1}.".format(params[key], key))
+                _("The payment processor returned a badly-typed value {0} for param {1}.".format(
+                    params['ccAuthReply_amount'], 'ccAuthReply_amount'))
             )
 
         if charged_amt == order.total_cost and valid_params['orderCurrency'] == order.currency:
             return {'accepted': True,
-                    'amt_charged': valid_params['ccAuthReply_amount'],
+                    'amt_charged': charged_amt,
                     'currency': valid_params['orderCurrency'],
                     'order': order}
         else:
@@ -275,7 +275,8 @@ def get_processor_exception_html(params, exception):
     return '<p class="error_msg">EXCEPTION!</p>'
 
 
-CARDTYPE_MAP = defaultdict(lambda:"UNKNOWN").update(
+CARDTYPE_MAP = defaultdict(lambda:"UNKNOWN")
+CARDTYPE_MAP.update(
     {
         '001': 'Visa',
         '002': 'MasterCard',
diff --git a/lms/djangoapps/shoppingcart/views.py b/lms/djangoapps/shoppingcart/views.py
index 85334df6a6..0d046b9a4b 100644
--- a/lms/djangoapps/shoppingcart/views.py
+++ b/lms/djangoapps/shoppingcart/views.py
@@ -82,7 +82,8 @@ def postpay_callback(request):
     If unsuccessful the order will be left untouched and HTML messages giving more detailed error info will be
     returned.
     """
-    result = process_postpay_callback(request)
+    params = request.POST.dict()
+    result = process_postpay_callback(params)
     if result['success']:
         return HttpResponseRedirect(reverse('shoppingcart.views.show_receipt', args=[result['order'].id]))
     else: