diff --git a/app/models/spree/calculator_decorator.rb b/app/models/spree/calculator_decorator.rb
index 33c32c901e..5d130d86aa 100644
--- a/app/models/spree/calculator_decorator.rb
+++ b/app/models/spree/calculator_decorator.rb
@@ -9,7 +9,7 @@ module Spree
         [object]
       elsif object.respond_to? :line_items
         object.line_items
-      elsif object.order.present?
+      elsif object.respond_to?(:order) && object.order.present?
         object.order.line_items
       else
         [object]
diff --git a/spec/models/spree/calculator_spec.rb b/spec/models/spree/calculator_spec.rb
new file mode 100644
index 0000000000..2aa8c5d0a8
--- /dev/null
+++ b/spec/models/spree/calculator_spec.rb
@@ -0,0 +1,44 @@
+require 'spec_helper'
+
+module Spree
+  describe Calculator do
+    let(:calculator) { Spree::Calculator.new }
+    let!(:enterprise) { create(:enterprise) }
+    let!(:order) { create(:order) }
+    let!(:shipment) { create(:shipment) }
+    let!(:line_item) { create(:line_item, order: order) }
+    let!(:line_item2) { create(:line_item, order: order) }
+
+    before do
+      order.line_items << line_item
+      order.line_items << line_item2
+      order.shipments = [shipment]
+    end
+
+    describe "#line_items_for" do
+      it "returns the line item if given a line item" do
+        result = calculator.__send__(:line_items_for, line_item)
+
+        expect(result).to eq [line_item]
+      end
+
+      it "returns line items if given an object with line items" do
+        result = calculator.__send__(:line_items_for, order)
+
+        expect(result).to eq [line_item, line_item2]
+      end
+
+      it "returns line items if given an object with an order" do
+        result = calculator.__send__(:line_items_for, shipment)
+
+        expect(result).to eq [line_item, line_item2]
+      end
+
+      it "returns the original object if given anything else" do
+        result = calculator.__send__(:line_items_for, enterprise)
+
+        expect(result).to eq [enterprise]
+      end
+    end
+  end
+end