diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index 1400abd225..5f29c8cf80 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -784,12 +784,13 @@ class Part(MPTTModel):
         """ Return the current number of parts currently being built
         """
 
-        quantity = self.active_builds.aggregate(quantity=Sum('quantity'))['quantity']
+        stock_items = self.stock_items.filter(is_building=True)
 
-        if quantity is None:
-            quantity = 0
+        query = stock_items.aggregate(
+            quantity=Coalesce(Sum('quantity'), Decimal(0))
+        )
 
-        return quantity
+        return query['quantity']
 
     def build_order_allocations(self):
         """
diff --git a/InvenTree/stock/models.py b/InvenTree/stock/models.py
index 3277137a25..fbdc1654f3 100644
--- a/InvenTree/stock/models.py
+++ b/InvenTree/stock/models.py
@@ -721,6 +721,10 @@ class StockItem(MPTTModel):
         if self.customer is not None:
             return False
 
+        # Not 'in stock' if it is building
+        if self.is_building:
+            return False
+
         # Not 'in stock' if the status code makes it unavailable
         if self.status in StockStatus.UNAVAILABLE_CODES:
             return False
diff --git a/InvenTree/stock/tests.py b/InvenTree/stock/tests.py
index 23cf6b3d02..135cb48f8b 100644
--- a/InvenTree/stock/tests.py
+++ b/InvenTree/stock/tests.py
@@ -47,6 +47,30 @@ class StockTest(TestCase):
         Part.objects.rebuild()
         StockItem.objects.rebuild()
 
+    def test_is_building(self):
+        """
+        Test that the is_building flag does not count towards stock.
+        """
+
+        part = Part.objects.get(pk=1)
+
+        # Record the total stock count
+        n = part.total_stock
+
+        StockItem.objects.create(part=part, quantity=5)
+
+        # And there should be *no* items being build
+        self.assertEqual(part.quantity_being_built, 0)
+
+        # Add some stock items which are "building"
+        for i in range(10):
+            item = StockItem.objects.create(part=part, quantity=10, is_building=True)
+
+        # The "is_building" quantity should not be counted here
+        self.assertEqual(part.total_stock, n + 5)
+
+        self.assertEqual(part.quantity_being_built, 100)
+
     def test_loc_count(self):
         self.assertEqual(StockLocation.objects.count(), 7)