diff --git a/app/models/concerns/line_item_stock_changes.rb b/app/models/concerns/line_item_stock_changes.rb
new file mode 100644
index 0000000000..a61bb21be3
--- /dev/null
+++ b/app/models/concerns/line_item_stock_changes.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+# Rails 5 introduced some breaking changes to these built-in methods, and the new versions
+# no longer work correctly in relation to decrementing stock with LineItems / VariantOverrides.
+# The following methods re-instate the pre-Rails-5 versions, which work as expected.
+# https://apidock.com/rails/v4.2.9/ActiveRecord/Persistence/increment%21
+# https://apidock.com/rails/v4.2.9/ActiveRecord/Persistence/decrement%21
+
+module LineItemStockChanges
+  extend ActiveSupport::Concern
+
+  def increment!(attribute, by = 1)
+    increment(attribute, by).update_attribute(attribute, self[attribute])
+  end
+
+  def decrement!(attribute, by = 1)
+    decrement(attribute, by).update_attribute(attribute, self[attribute])
+  end
+end
diff --git a/app/models/spree/line_item.rb b/app/models/spree/line_item.rb
index c2da5814d6..6b502e1bcd 100644
--- a/app/models/spree/line_item.rb
+++ b/app/models/spree/line_item.rb
@@ -6,6 +6,7 @@ require 'variant_units/variant_and_line_item_naming'
 module Spree
   class LineItem < ActiveRecord::Base
     include VariantUnits::VariantAndLineItemNaming
+    include LineItemStockChanges
     include LineItemBasedAdjustmentHandling
 
     belongs_to :order, class_name: "Spree::Order", inverse_of: :line_items