diff --git a/app/controllers/spree/orders_controller_decorator.rb b/app/controllers/spree/orders_controller_decorator.rb
index 54b08aed8b..7d221ddbeb 100644
--- a/app/controllers/spree/orders_controller_decorator.rb
+++ b/app/controllers/spree/orders_controller_decorator.rb
@@ -224,22 +224,27 @@ Spree::OrdersController.class_eval do
     n == Float::INFINITY ? 2147483647 : n
   end
 
+  # If a specific order is mentioned, check that it is COMPLETE, that changes
+  # are allowed and that the user has access. Return nil if not.
   def order_to_update
-    order = Spree::Order.complete.find_by_number(params[:id])
-    return order if order.andand.changes_allowed? && can?(:update, order)
-    current_order
+    return @order_to_update if defined? @order_to_update
+    return @order_to_update = current_order unless params[:id]
+    @order_to_update = begin
+      order = Spree::Order.complete.find_by_number(params[:id])
+      order = nil unless order.andand.changes_allowed? && can?(:update, order)
+      order
+    end
   end
 
   def check_at_least_one_line_item
-    order = order_to_update
-    return unless order.complete?
+    return unless order_to_update.andand.complete?
 
     items = params[:order][:line_items_attributes]
     .andand.select{ |k,attrs| attrs["quantity"].to_i > 0 }
 
     if items.empty?
       flash[:error] = I18n.t(:orders_cannot_remove_the_final_item)
-      redirect_to order_path(order)
+      redirect_to order_path(order_to_update)
     end
   end
 end
diff --git a/spec/controllers/spree/orders_controller_spec.rb b/spec/controllers/spree/orders_controller_spec.rb
index 4ec0c63eed..e7b5a7e12a 100644
--- a/spec/controllers/spree/orders_controller_spec.rb
+++ b/spec/controllers/spree/orders_controller_spec.rb
@@ -323,8 +323,8 @@ describe Spree::OrdersController do
       context "and the order is not complete" do
         let!(:order) { create(:order) }
 
-        it "returns the current_order" do
-          expect(controller.send(:order_to_update)).to eq current_order
+        it "returns nil" do
+          expect(controller.send(:order_to_update)).to eq nil
         end
       end
 
@@ -334,8 +334,8 @@ describe Spree::OrdersController do
         context "and the user doesn't have permisson to 'update' the order" do
           before { allow(controller).to receive(:can?).with(:update, order) { false } }
 
-          it "returns the current_order" do
-            expect(controller.send(:order_to_update)).to eq current_order
+          it "returns nil" do
+            expect(controller.send(:order_to_update)).to eq nil
           end
         end
 
@@ -344,8 +344,8 @@ describe Spree::OrdersController do
 
           context "and the order is not editable" do
 
-            it "returns the current_order" do
-              expect(controller.send(:order_to_update)).to eq current_order
+            it "returns nil" do
+              expect(controller.send(:order_to_update)).to eq nil
             end
           end