diff --git a/core/app/models/spree/order_merger.rb b/core/app/models/spree/order_merger.rb
index 4f79ba841b..c3414a6c5c 100644
--- a/core/app/models/spree/order_merger.rb
+++ b/core/app/models/spree/order_merger.rb
@@ -115,8 +115,8 @@ def handle_merge(current_line_item, other_order_line_item)
         current_line_item.quantity += other_order_line_item.quantity
         handle_error(current_line_item) unless current_line_item.save
       else
-        order.line_items << other_order_line_item
-        handle_error(other_order_line_item) unless other_order_line_item.save
+        new_line_item = order.line_items.build(other_order_line_item.attributes.except("id"))
+        handle_error(new_line_item) unless new_line_item.save
       end
     end
 
diff --git a/core/spec/models/spree/order_merger_spec.rb b/core/spec/models/spree/order_merger_spec.rb
index e48d4ded1b..11e0971de1 100644
--- a/core/spec/models/spree/order_merger_spec.rb
+++ b/core/spec/models/spree/order_merger_spec.rb
@@ -141,6 +141,21 @@ module Spree
         expect(order_1.line_items.pluck(:quantity)).to match_array([1, 1])
         expect(order_1.line_items.pluck(:variant_id)).to match_array([variant.id, variant_2.id])
       end
+
+      context "with line item promotion applied to order 2" do
+        let!(:promotion) { create(:promotion, :with_line_item_adjustment, apply_automatically: true) }
+
+        before do
+          Spree::PromotionHandler::Cart.new(order_2).activate
+          expect(order_2.line_items.flat_map(&:adjustments)).not_to be_empty
+        end
+
+        it "does not carry a line item adjustments with the wrong order ID over" do
+          subject.merge!(order_2)
+          expect { order_2.reload }.to raise_exception(ActiveRecord::RecordNotFound)
+          expect(order_1.line_items.flat_map(&:adjustments)).to be_empty
+        end
+      end
     end
 
     context "merging together orders with invalid line items" do