diff --git a/InvenTree/InvenTree/filters.py b/InvenTree/InvenTree/filters.py
index fbd1e53fe0..94e6e1765b 100644
--- a/InvenTree/InvenTree/filters.py
+++ b/InvenTree/InvenTree/filters.py
@@ -34,8 +34,6 @@ class InvenTreeOrderingFilter(OrderingFilter):
             Ordering fields should be mapped to separate fields
             """
 
-            idx = 0
-
             ordering_initial = ordering
             ordering = []
 
diff --git a/InvenTree/build/serializers.py b/InvenTree/build/serializers.py
index f2bf97cf7f..5a64bda0a0 100644
--- a/InvenTree/build/serializers.py
+++ b/InvenTree/build/serializers.py
@@ -72,7 +72,7 @@ class BuildSerializer(InvenTreeModelSerializer):
             )
         )
 
-        # Annotate with a "integer" version of the reference field, to be used for natural sorting
+        # Annotate with an "integer" version of the reference field, to be used for natural sorting
         queryset = queryset.annotate(
             integer_ref=Cast('reference', output_field=IntegerField())
         )
diff --git a/InvenTree/order/api.py b/InvenTree/order/api.py
index af30a3a5c5..a451f05ac8 100644
--- a/InvenTree/order/api.py
+++ b/InvenTree/order/api.py
@@ -152,9 +152,13 @@ class POList(generics.ListCreateAPIView):
     filter_backends = [
         rest_filters.DjangoFilterBackend,
         filters.SearchFilter,
-        filters.OrderingFilter,
+        InvenTreeOrderingFilter,
     ]
 
+    ordering_field_aliases = {
+        'reference': ['integer_ref', 'reference'],
+    }
+
     filter_fields = [
         'supplier',
     ]
@@ -504,9 +508,13 @@ class SOList(generics.ListCreateAPIView):
     filter_backends = [
         rest_filters.DjangoFilterBackend,
         filters.SearchFilter,
-        filters.OrderingFilter,
+        InvenTreeOrderingFilter,
     ]
 
+    ordering_field_aliases = {
+        'reference': ['integer_ref', 'reference'],
+    }
+
     filter_fields = [
         'customer',
     ]
diff --git a/InvenTree/order/serializers.py b/InvenTree/order/serializers.py
index 40cd2def58..bcc1791db4 100644
--- a/InvenTree/order/serializers.py
+++ b/InvenTree/order/serializers.py
@@ -4,6 +4,7 @@ JSON serializers for the Order API
 
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
+from django.db.models.fields import IntegerField
 
 from django.utils.translation import ugettext_lazy as _
 
@@ -11,6 +12,7 @@ from django.core.exceptions import ValidationError as DjangoValidationError
 from django.db import models, transaction
 from django.db.models import Case, When, Value
 from django.db.models import BooleanField, ExpressionWrapper, F
+from django.db.models.functions import Cast
 
 from rest_framework import serializers
 from rest_framework.serializers import ValidationError
@@ -73,6 +75,11 @@ class POSerializer(InvenTreeModelSerializer):
             )
         )
 
+        # Annotate with an "integer" version of the reference field, to be used for natural sorting
+        queryset = queryset.annotate(
+            integer_ref=Cast('reference', output_field=IntegerField())
+        )
+
         return queryset
 
     supplier_detail = CompanyBriefSerializer(source='supplier', many=False, read_only=True)
@@ -428,6 +435,11 @@ class SalesOrderSerializer(InvenTreeModelSerializer):
             )
         )
 
+        # Annotate with an "integer" version of the reference field, to be used for natural sorting
+        queryset = queryset.annotate(
+            integer_ref=Cast('reference', output_field=IntegerField())
+        )
+
         return queryset
 
     customer_detail = CompanyBriefSerializer(source='customer', many=False, read_only=True)