diff --git a/InvenTree/company/models.py b/InvenTree/company/models.py
index 33841d59db..069ecb0ad6 100644
--- a/InvenTree/company/models.py
+++ b/InvenTree/company/models.py
@@ -327,7 +327,7 @@ class SupplierPart(models.Model):
         if q is None or r is None:
             return 0
         else:
-            return q - r
+            return max(q-r, 0)
     
 
     def purchase_orders(self):
diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index f1294a972d..6749fa0ad6 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -809,7 +809,7 @@ class Part(models.Model):
     def on_order(self):
         """ Return the total number of items on order for this part. """
 
-        return sum([part.on_order() for part in self.supplier_parts.all()])
+        return sum([part.on_order() for part in self.supplier_parts.all().prefetch_related('purchase_order_line_items')])
 
 
 def attach_file(instance, filename):