diff --git a/InvenTree/build/models.py b/InvenTree/build/models.py
index c42f52ec1a..e843422f63 100644
--- a/InvenTree/build/models.py
+++ b/InvenTree/build/models.py
@@ -584,7 +584,7 @@ class BuildItem(models.Model):
         errors = {}
 
         try:
-            if self.stock_item.part not in self.build.part.required_parts():
+            if self.stock_item.part not in self.build.part.getRequiredParts(recursive=False):
                 errors['stock_item'] = [_("Selected stock item not found in BOM for part '{p}'".format(p=self.build.part.full_name))]
             
             if self.quantity > self.stock_item.quantity:
diff --git a/InvenTree/build/views.py b/InvenTree/build/views.py
index 70905b1b4f..ff1befcfc3 100644
--- a/InvenTree/build/views.py
+++ b/InvenTree/build/views.py
@@ -493,7 +493,7 @@ class BuildItemDelete(AjaxDeleteView):
 
 class BuildItemCreate(AjaxCreateView):
     """
-    View for allocating a StockItems to a build output.    
+    View for allocating a StockItems to a build output.
     """
 
     model = BuildItem
@@ -591,13 +591,20 @@ class BuildItemCreate(AjaxCreateView):
                         pass
 
                     # Exclude StockItem objects which are already allocated to this build and part
-                    stock_filter = stock_filter.exclude(id__in=[item.stock_item.id for item in BuildItem.objects.filter(build=build_id, stock_item__part=part_id)])
+                    stock_filter = stock_filter.exclude(
+                        id__in=[
+                            item.stock_item.id for item in BuildItem.objects.filter(build=build_id, stock_item__part=part_id)
+                        ]
+                    )
 
             except Part.DoesNotExist:
                 self.part = None
                 pass
 
-        form.fields['stock_item'].query = stock_filter
+        else:
+            self.part = None
+
+        form.fields['stock_item'].queryset = stock_filter
 
         self.available_stock = stock_filter.all()
 
@@ -708,13 +715,12 @@ class BuildItemEdit(AjaxUpdateView):
         }
 
     def get_form(self):
-        """ Create form for editing a BuildItem.
+        """
+        Create form for editing a BuildItem.
 
         - Limit the StockItem options to items that match the part
         """
 
-        build_item = self.get_object()
-
         form = super(BuildItemEdit, self).get_form()
 
         # Hide fields which we do not wish the user to edit
diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index b289b3e0ad..ddf612da92 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -931,13 +931,26 @@ class Part(MPTTModel):
 
         self.bom_items.all().delete()
 
-    def required_parts(self):
-        """ Return a list of parts required to make this part (list of BOM items) """
-        parts = []
+    def getRequiredParts(self, recursive=False, parts=set()):
+        """
+        Return a list of parts required to make this part (i.e. BOM items).
+
+        Args:
+            recursive: If True iterate down through sub-assemblies
+            parts: Set of parts already found (to prevent recursion issues)
+        """
+
+        for bom_item in self.bom_items.all().select_related('sub_part'):
+
+            sub_part = bom_item.sub_part
+
+            if sub_part not in parts:
+
+                parts.add(sub_part)
+
+                if recursive:
+                    sub_part.getRequiredParts(recursive=True, parts=parts)
 
-        for bom in self.bom_items.all().select_related('sub_part'):
-            parts.append(bom.sub_part)
-        
         return parts
 
     def get_allowed_bom_items(self):
diff --git a/InvenTree/part/views.py b/InvenTree/part/views.py
index a1ce33df51..c7ad280d8e 100644
--- a/InvenTree/part/views.py
+++ b/InvenTree/part/views.py
@@ -2127,7 +2127,7 @@ class BomItemCreate(AjaxCreateView):
             query = query.filter(active=True)
             
             # Eliminate any options that are already in the BOM!
-            query = query.exclude(id__in=[item.id for item in part.required_parts()])
+            query = query.exclude(id__in=[item.id for item in part.getRequiredParts()])
             
             form.fields['sub_part'].queryset = query
 
@@ -2195,7 +2195,7 @@ class BomItemEdit(AjaxUpdateView):
             except ValueError:
                 sub_part_id = -1
 
-            existing = [item.pk for item in part.required_parts()]
+            existing = [item.pk for item in part.getRequiredParts()]
 
             if sub_part_id in existing:
                 existing.remove(sub_part_id)