diff --git a/app/controllers/spree/admin/payment_methods_controller.rb b/app/controllers/spree/admin/payment_methods_controller.rb
index e467e8356c..077cddbca8 100644
--- a/app/controllers/spree/admin/payment_methods_controller.rb
+++ b/app/controllers/spree/admin/payment_methods_controller.rb
@@ -7,7 +7,6 @@ module Spree
       before_action :load_data
       before_action :validate_payment_method_provider, only: [:create]
       before_action :load_hubs, only: [:new, :edit, :update]
-      before_action :validate_calculator_preferred_value, only: [:update]
 
       respond_to :html
 
@@ -17,6 +16,10 @@ module Spree
         @payment_method = payment_method_class.constantize.new(base_params)
         @object = @payment_method
 
+        if !base_params["calculator_type"] && gateway_params["calculator_type"]
+          @payment_method.calculator_type = gateway_params["calculator_type"]
+        end
+
         load_hubs
 
         if @payment_method.save
@@ -44,6 +47,7 @@ module Spree
           redirect_to spree.edit_admin_payment_method_path(@payment_method)
         else
           respond_with(@payment_method)
+          clear_preference_cache
         end
       end
 
@@ -182,33 +186,23 @@ module Spree
             end
           end
 
+          # Ensure the calculator to be updated is the correct type
+          if params_for_update["calculator_type"] && params_for_update["calculator_attributes"]
+            add_type_to_calculator_attributes(params_for_update)
+          end
+
           params_for_update
         end
       end
 
-      def validate_calculator_preferred_value
-        return if calculator_preferred_values.all? do |value|
-          preferred_value_from_params = gateway_params.dig(:calculator_attributes, value)
-          preferred_value_from_params.nil? || Float(preferred_value_from_params,
-                                                    exception: false)
+      def clear_preference_cache
+        @payment_method.calculator.preferences.each_key do |key|
+          Rails.cache.delete(@payment_method.calculator.preference_cache_key(key))
         end
-
-        flash[:error] = I18n.t(:calculator_preferred_value_error)
-        redirect_to spree.edit_admin_payment_method_path(@payment_method)
       end
 
-      def calculator_preferred_values
-        [
-          :preferred_amount,
-          :preferred_flat_percent,
-          :preferred_flat_percent,
-          :preferred_first_item,
-          :preferred_additional_item,
-          :preferred_max_items,
-          :preferred_normal_amount,
-          :preferred_discount_amount,
-          :preferred_minimal_amount
-        ]
+      def add_type_to_calculator_attributes(hash)
+        hash["calculator_attributes"]["type"] = hash["calculator_type"]
       end
     end
   end
diff --git a/app/helpers/spree/admin/base_helper.rb b/app/helpers/spree/admin/base_helper.rb
index 3983cf3fda..d527b04d1d 100644
--- a/app/helpers/spree/admin/base_helper.rb
+++ b/app/helpers/spree/admin/base_helper.rb
@@ -29,8 +29,8 @@ module Spree
 
       def preference_field_tag(name, value, options)
         case options[:type]
-        when :integer
-          text_field_tag(name, value, preference_field_options(options))
+        when :integer, :decimal
+          number_field_tag(name, value, preference_field_options(options))
         when :boolean
           hidden_field_tag(name, 0) +
             check_box_tag(name, 1, value, preference_field_options(options))
@@ -49,8 +49,8 @@ module Spree
 
       def preference_field_for(form, field, options, object)
         case options[:type]
-        when :integer
-          form.text_field(field, preference_field_options(options))
+        when :integer, :decimal
+          form.number_field(field, preference_field_options(options))
         when :boolean
           form.check_box(field, preference_field_options(options))
         when :string
@@ -80,26 +80,24 @@ module Spree
       end
 
       def preference_field_options(options)
-        field_options = case options[:type]
-                        when :integer
-                          { size: 10,
-                            class: 'input_integer' }
-                        when :boolean
-                          {}
-                        when :string
-                          { size: 10,
-                            class: 'input_string fullwidth' }
-                        when :password
-                          { size: 10,
-                            class: 'password_string fullwidth' }
-                        when :text
-                          { rows: 15,
-                            cols: 85,
-                            class: 'fullwidth' }
-                        else
-                          { size: 10,
-                            class: 'input_string fullwidth' }
-                        end
+        field_options =
+          case options[:type]
+          when :integer
+            { size: 10, class: 'input_integer', step: 1 }
+          when :decimal
+            # Allow any number of decimal places
+            { size: 10, class: 'input_integer', step: :any }
+          when :boolean
+            {}
+          when :string
+            { size: 10, class: 'input_string fullwidth' }
+          when :password
+            { size: 10, class: 'password_string fullwidth' }
+          when :text
+            { rows: 15, cols: 85, class: 'fullwidth' }
+          else
+            { size: 10, class: 'input_string fullwidth' }
+          end
 
         field_options.merge!(
           readonly: options[:readonly],
diff --git a/app/models/calculator/flat_percent_item_total.rb b/app/models/calculator/flat_percent_item_total.rb
index d4c2067444..f0d7a330e5 100644
--- a/app/models/calculator/flat_percent_item_total.rb
+++ b/app/models/calculator/flat_percent_item_total.rb
@@ -1,14 +1,11 @@
 # frozen_string_literal: false
 
-require 'spree/localized_number'
-
 module Calculator
   class FlatPercentItemTotal < Spree::Calculator
-    extend Spree::LocalizedNumber
-
     preference :flat_percent, :decimal, default: 0
 
-    localize_number :preferred_flat_percent
+    validates :preferred_flat_percent,
+              numericality: true
 
     def self.description
       Spree.t(:flat_percent)
diff --git a/app/models/calculator/flat_percent_per_item.rb b/app/models/calculator/flat_percent_per_item.rb
index f9e197c594..e078340d7b 100644
--- a/app/models/calculator/flat_percent_per_item.rb
+++ b/app/models/calculator/flat_percent_per_item.rb
@@ -1,18 +1,15 @@
 # frozen_string_literal: true
 
-require 'spree/localized_number'
-
 class Calculator::FlatPercentPerItem < Spree::Calculator
   # Spree's FlatPercentItemTotal calculator sums all amounts, and then calculates a percentage
   # on them.
   # In the cart, we display line item individual amounts rounded, so to have consistent
   # calculations we do the same internally. Here, we round adjustments at the individual
   # item level first, then multiply by the item quantity.
-  extend Spree::LocalizedNumber
-
   preference :flat_percent, :decimal, default: 0
 
-  localize_number :preferred_flat_percent
+  validates :preferred_flat_percent,
+            numericality: true
 
   def self.description
     I18n.t(:flat_percent_per_item)
diff --git a/app/models/calculator/flat_rate.rb b/app/models/calculator/flat_rate.rb
index a8ab771b98..a130b88c17 100644
--- a/app/models/calculator/flat_rate.rb
+++ b/app/models/calculator/flat_rate.rb
@@ -1,14 +1,11 @@
 # frozen_string_literal: false
 
-require 'spree/localized_number'
-
 module Calculator
   class FlatRate < Spree::Calculator
-    extend Spree::LocalizedNumber
-
     preference :amount, :decimal, default: 0
 
-    localize_number :preferred_amount
+    validates :preferred_amount,
+              numericality: true
 
     def self.description
       I18n.t(:flat_rate_per_order)
diff --git a/app/models/calculator/flexi_rate.rb b/app/models/calculator/flexi_rate.rb
index bb6bb1ff9b..1959aec67e 100644
--- a/app/models/calculator/flexi_rate.rb
+++ b/app/models/calculator/flexi_rate.rb
@@ -1,17 +1,14 @@
 # frozen_string_literal: false
 
-require 'spree/localized_number'
-
 module Calculator
   class FlexiRate < Spree::Calculator
-    extend Spree::LocalizedNumber
-
     preference :first_item,      :decimal, default: 0.0
     preference :additional_item, :decimal, default: 0.0
     preference :max_items,       :integer, default: 0
 
-    localize_number :preferred_first_item,
-                    :preferred_additional_item
+    validates :preferred_first_item,
+              :preferred_additional_item,
+              numericality: true
 
     def self.description
       I18n.t(:flexible_rate)
diff --git a/app/models/calculator/per_item.rb b/app/models/calculator/per_item.rb
index f8cce8e7a7..0df18ae3d4 100644
--- a/app/models/calculator/per_item.rb
+++ b/app/models/calculator/per_item.rb
@@ -1,14 +1,11 @@
 # frozen_string_literal: false
 
-require 'spree/localized_number'
-
 module Calculator
   class PerItem < Spree::Calculator
-    extend Spree::LocalizedNumber
-
     preference :amount, :decimal, default: 0
 
-    localize_number :preferred_amount
+    validates :preferred_amount,
+              numericality: true
 
     def self.description
       I18n.t(:flat_rate_per_item)
diff --git a/app/models/calculator/price_sack.rb b/app/models/calculator/price_sack.rb
index 910b663b1d..217928581f 100644
--- a/app/models/calculator/price_sack.rb
+++ b/app/models/calculator/price_sack.rb
@@ -1,18 +1,15 @@
 # frozen_string_literal: false
 
-require 'spree/localized_number'
-
 module Calculator
   class PriceSack < Spree::Calculator
-    extend Spree::LocalizedNumber
-
     preference :minimal_amount, :decimal, default: 0
     preference :normal_amount, :decimal, default: 0
     preference :discount_amount, :decimal, default: 0
 
-    localize_number :preferred_minimal_amount,
-                    :preferred_normal_amount,
-                    :preferred_discount_amount
+    validates :preferred_minimal_amount,
+              :preferred_normal_amount,
+              :preferred_discount_amount,
+              numericality: true
 
     def self.description
       I18n.t(:price_sack)
diff --git a/app/models/spree/payment_method.rb b/app/models/spree/payment_method.rb
index f90a526f7c..bbb9d4053d 100644
--- a/app/models/spree/payment_method.rb
+++ b/app/models/spree/payment_method.rb
@@ -17,6 +17,7 @@ module Spree
 
     validates :name, presence: true
     validate :distributor_validation
+    validates_associated :calculator
 
     after_initialize :init
 
@@ -40,9 +41,8 @@ module Spree
       where(id: non_unique_matches.map(&:id))
     }
 
-    scope :for_distributor, lambda { |distributor|
-      joins(:distributors).
-        where('enterprises.id = ?', distributor)
+    scope :for_distributor, ->(distributor) {
+      joins(:distributors).where('enterprises.id = ?', distributor)
     }
 
     scope :for_subscriptions, -> { where(type: Subscription::ALLOWED_PAYMENT_METHOD_TYPES) }
diff --git a/app/models/spree/preference.rb b/app/models/spree/preference.rb
index dfef2a146d..ea2c63688c 100644
--- a/app/models/spree/preference.rb
+++ b/app/models/spree/preference.rb
@@ -22,7 +22,8 @@ module Spree
         when :password
           self[:value].to_s
         when :decimal
-          BigDecimal(self[:value].to_s).round(2, BigDecimal::ROUND_HALF_UP)
+          BigDecimal(self[:value].to_s, exception: false)&.round(2, BigDecimal::ROUND_HALF_UP) ||
+            self[:value]
         when :integer
           self[:value].to_i
         when :boolean
diff --git a/app/models/spree/preferences/preferable.rb b/app/models/spree/preferences/preferable.rb
index 2c0f61b2e2..af775ab37d 100644
--- a/app/models/spree/preferences/preferable.rb
+++ b/app/models/spree/preferences/preferable.rb
@@ -117,7 +117,7 @@ module Spree
           value.to_s
         when :decimal
           value = 0 if value.blank?
-          BigDecimal(value.to_s).round(2, BigDecimal::ROUND_HALF_UP)
+          BigDecimal(value.to_s, exception: false)&.round(2, BigDecimal::ROUND_HALF_UP) || value
         when :integer
           value.to_i
         when :boolean
diff --git a/app/views/spree/admin/payment_methods/_providers.html.haml b/app/views/spree/admin/payment_methods/_providers.html.haml
index aa1fce7fe8..b25a7b09c5 100644
--- a/app/views/spree/admin/payment_methods/_providers.html.haml
+++ b/app/views/spree/admin/payment_methods/_providers.html.haml
@@ -3,6 +3,6 @@
     .alpha.four.columns
       = label :payment_method, :type, t('.provider')
     .omega.twelve.columns
-      = collection_select(:payment_method, :type, @providers, :to_s, :clean_name, (!@object.persisted? ? { :selected => "Spree::PaymentMethod::Check"} : {}), { class: 'select2 fullwidth', 'provider-prefs-for' => "#{@object.id}"})
+      = collection_select(:payment_method, :type, @providers, :to_s, :clean_name, {}, { class: 'select2 fullwidth', 'provider-prefs-for' => "#{@object.id}"})
 
   %div{"ng-include" => "include_html" }
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 42e86b3243..c8a9ab96fc 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -79,6 +79,17 @@ en:
         orders_close_at: Close date
       variant_override:
         count_on_hand: "On Hand"
+      spree/payment_method/calculator:
+        preferred_flat_percent: "Calculator Flat Percent:"
+        preferred_amount: "Calculator Amount:"
+        preferred_first_item: "Calculator First Item:"
+        preferred_additional_item: "Calculator Additional Item Cost:"
+        preferred_max_items: "Calculator Max Items:"
+        preferred_minimal_amount: "Calculator Minimal Amount:"
+        preferred_normal_amount: "Calculator Normal Amount:"
+        preferred_discount_amount: "Calculator Discount Amount:"
+        preferred_unit_from_list: "Calculator Unit From List:"
+        preferred_per_unit: "Calculator Per Unit:"
     errors:
       models:
         spree/user:
diff --git a/lib/spree/localized_number.rb b/lib/spree/localized_number.rb
index 77270d49ee..a1ba18accd 100644
--- a/lib/spree/localized_number.rb
+++ b/lib/spree/localized_number.rb
@@ -21,7 +21,7 @@ module Spree
           elsif Spree::Config.enable_localized_number?
             @invalid_localized_number ||= []
             @invalid_localized_number << attribute
-            number = nil
+            number = nil unless is_a?(Spree::Calculator)
           end
           if has_attribute?(attribute)
             # In this case it's a regular AR attribute with standard setters
@@ -44,7 +44,8 @@ module Spree
 
     def self.valid_localizable_number?(number)
       return true unless number.is_a?(String) || number.respond_to?(:to_d)
-      return false if number.to_s =~ /[.,]\d{2}[.,]/
+      # Invalid if only two digits between dividers, or if any non-number characters
+      return false if number.to_s =~ /[.,]\d{2}[.,]/ || number.to_s =~ /[^0-9,.]+/
 
       true
     end
diff --git a/lib/tasks/sample_data/payment_method_factory.rb b/lib/tasks/sample_data/payment_method_factory.rb
index 4febf09fa4..ba545b2d11 100644
--- a/lib/tasks/sample_data/payment_method_factory.rb
+++ b/lib/tasks/sample_data/payment_method_factory.rb
@@ -53,8 +53,8 @@ module SampleData
         environment: Rails.env,
         distributor_ids: [enterprise.id]
       )
-      calculator.calculable = payment_method
-      calculator.save!
+      payment_method.calculator = calculator
+      payment_method.save!
     end
   end
 end
diff --git a/spec/base_spec_helper.rb b/spec/base_spec_helper.rb
index cc4dc35e65..19206bd0b5 100644
--- a/spec/base_spec_helper.rb
+++ b/spec/base_spec_helper.rb
@@ -142,6 +142,9 @@ RSpec.configure do |config|
 
   config.infer_spec_type_from_file_location!
 
+  # You can use `rspec -n` to run only failed specs.
+  config.example_status_persistence_file_path = "tmp/rspec-status.txt"
+
   # Helpers
   config.include FactoryBot::Syntax::Methods
   config.include JsonSpec::Helpers
diff --git a/spec/lib/spree/localized_number_spec.rb b/spec/lib/spree/localized_number_spec.rb
index b13f8ddf6e..bafe0c822d 100644
--- a/spec/lib/spree/localized_number_spec.rb
+++ b/spec/lib/spree/localized_number_spec.rb
@@ -59,5 +59,11 @@ describe Spree::LocalizedNumber do
         expect(described_class.valid_localizable_number?(1599.99)).to eql true
       end
     end
+
+    context "with letters" do
+      it "returns false" do
+        expect(described_class.valid_localizable_number?('invalid')).to eql false
+      end
+    end
   end
 end
diff --git a/spec/models/calculator/flat_percent_item_total_spec.rb b/spec/models/calculator/flat_percent_item_total_spec.rb
index 7d34211259..a0c57c6266 100644
--- a/spec/models/calculator/flat_percent_item_total_spec.rb
+++ b/spec/models/calculator/flat_percent_item_total_spec.rb
@@ -8,14 +8,12 @@ describe Calculator::FlatPercentItemTotal do
 
   before { allow(calculator).to receive_messages preferred_flat_percent: 10 }
 
+  it { is_expected.to validate_numericality_of(:preferred_flat_percent) }
+
   it "computes amount correctly for a single line item" do
     expect(calculator.compute(line_item)).to eq(1.0)
   end
 
-  context "extends LocalizedNumber" do
-    it_behaves_like "a model using the LocalizedNumber module", [:preferred_flat_percent]
-  end
-
   it "computes amount correctly for a given OrderManagement::Stock::Package" do
     order = double(:order, line_items: [line_item] )
     package = double(:package, order: order)
diff --git a/spec/models/calculator/flat_percent_per_item_spec.rb b/spec/models/calculator/flat_percent_per_item_spec.rb
index 6f16a9fe6a..ac873a0ba7 100644
--- a/spec/models/calculator/flat_percent_per_item_spec.rb
+++ b/spec/models/calculator/flat_percent_per_item_spec.rb
@@ -5,6 +5,8 @@ require 'spec_helper'
 describe Calculator::FlatPercentPerItem do
   let(:calculator) { Calculator::FlatPercentPerItem.new preferred_flat_percent: 20 }
 
+  it { is_expected.to validate_numericality_of(:preferred_flat_percent) }
+
   it "calculates for a simple line item" do
     line_item = Spree::LineItem.new price: 50, quantity: 2
     expect(calculator.compute(line_item)).to eq 20
@@ -14,8 +16,4 @@ describe Calculator::FlatPercentPerItem do
     line_item = Spree::LineItem.new price: 0.86, quantity: 8
     expect(calculator.compute(line_item)).to eq 1.36
   end
-
-  context "extends LocalizedNumber" do
-    it_behaves_like "a model using the LocalizedNumber module", [:preferred_flat_percent]
-  end
 end
diff --git a/spec/models/calculator/flat_rate_spec.rb b/spec/models/calculator/flat_rate_spec.rb
index cb0cce62d2..92eaa864d0 100644
--- a/spec/models/calculator/flat_rate_spec.rb
+++ b/spec/models/calculator/flat_rate_spec.rb
@@ -7,7 +7,5 @@ describe Calculator::FlatRate do
 
   before { allow(calculator).to receive_messages preferred_amount: 10 }
 
-  context "extends LocalizedNumber" do
-    it_behaves_like "a model using the LocalizedNumber module", [:preferred_amount]
-  end
+  it { is_expected.to validate_numericality_of(:preferred_amount) }
 end
diff --git a/spec/models/calculator/flexi_rate_spec.rb b/spec/models/calculator/flexi_rate_spec.rb
index 81bbc95ee6..e5a777a412 100644
--- a/spec/models/calculator/flexi_rate_spec.rb
+++ b/spec/models/calculator/flexi_rate_spec.rb
@@ -12,6 +12,9 @@ describe Calculator::FlexiRate do
     )
   end
 
+  it { is_expected.to validate_numericality_of(:preferred_first_item) }
+  it { is_expected.to validate_numericality_of(:preferred_additional_item) }
+
   context 'when nb of items ordered is above preferred max' do
     let(:quantity) { 4.0 }
 
@@ -32,9 +35,4 @@ describe Calculator::FlexiRate do
     Calculator::FlexiRate.new(preferred_first_item: 1, preferred_additional_item: 1,
                               preferred_max_items: 1)
   end
-
-  context "extends LocalizedNumber" do
-    it_behaves_like "a model using the LocalizedNumber module",
-                    [:preferred_first_item, :preferred_additional_item]
-  end
 end
diff --git a/spec/models/calculator/per_item_spec.rb b/spec/models/calculator/per_item_spec.rb
index cde6cae8f5..914ca33dfa 100644
--- a/spec/models/calculator/per_item_spec.rb
+++ b/spec/models/calculator/per_item_spec.rb
@@ -7,12 +7,10 @@ describe Calculator::PerItem do
   let(:shipping_calculable) { double(:calculable) }
   let(:line_item) { build_stubbed(:line_item, quantity: 5) }
 
+  it { is_expected.to validate_numericality_of(:preferred_amount) }
+
   it "correctly calculates on a single line item object" do
     allow(calculator).to receive_messages(calculable: shipping_calculable)
     expect(calculator.compute(line_item).to_f).to eq(50) # 5 x 10
   end
-
-  context "extends LocalizedNumber" do
-    it_behaves_like "a model using the LocalizedNumber module", [:preferred_amount]
-  end
 end
diff --git a/spec/models/calculator/price_sack_spec.rb b/spec/models/calculator/price_sack_spec.rb
index 0034b20963..771b8428ec 100644
--- a/spec/models/calculator/price_sack_spec.rb
+++ b/spec/models/calculator/price_sack_spec.rb
@@ -12,6 +12,10 @@ describe Calculator::PriceSack do
   end
   let(:line_item) { build_stubbed(:line_item, price: price, quantity: 2) }
 
+  it { is_expected.to validate_numericality_of(:preferred_minimal_amount) }
+  it { is_expected.to validate_numericality_of(:preferred_normal_amount) }
+  it { is_expected.to validate_numericality_of(:preferred_discount_amount) }
+
   context 'when the order amount is below preferred minimal' do
     let(:price) { 2 }
 
@@ -75,10 +79,4 @@ describe Calculator::PriceSack do
       end
     end
   end
-
-  context "extends LocalizedNumber" do
-    it_behaves_like "a model using the LocalizedNumber module",
-                    [:preferred_minimal_amount, :preferred_normal_amount,
-                     :preferred_discount_amount]
-  end
 end
diff --git a/spec/models/spree/preference_spec.rb b/spec/models/spree/preference_spec.rb
index 780434f768..0eb32f9837 100644
--- a/spec/models/spree/preference_spec.rb
+++ b/spec/models/spree/preference_spec.rb
@@ -11,7 +11,7 @@ describe Spree::Preference do
     expect(@preference).to be_valid
   end
 
-  describe "type coversion for values" do
+  describe "type conversion for values" do
     def round_trip_preference(key, value, value_type)
       p = Spree::Preference.new
       p.value = value
@@ -58,6 +58,15 @@ describe Spree::Preference do
       expect(pref.value_type).to eq value_type.to_s
     end
 
+    it "incovertible :decimal" do
+      value_type = :decimal
+      value = "invalid"
+      key = "decimal_key"
+      pref = round_trip_preference(key, value, value_type)
+      expect(pref.value).to eq value
+      expect(pref.value_type).to eq value_type.to_s
+    end
+
     it ":string" do
       value_type = :string
       value = "This is a string"
diff --git a/spec/models/spree/preferences/preferable_spec.rb b/spec/models/spree/preferences/preferable_spec.rb
index 8b7edba9f0..e95e069de0 100644
--- a/spec/models/spree/preferences/preferable_spec.rb
+++ b/spec/models/spree/preferences/preferable_spec.rb
@@ -165,6 +165,13 @@ describe Spree::Preferences::Preferable do
         @a.set_preference(:if_decimal, '')
         expect(@a.preferences[:if_decimal]).to eq 0.0
       end
+
+      context "when the value cannot be converted to BigDecimal" do
+        it "returns the original value" do
+          @a.set_preference(:if_decimal, "invalid")
+          expect(@a.preferences[:if_decimal]).to eq "invalid"
+        end
+      end
     end
 
     context "converts boolean preferences to boolean values" do
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index da264f58e3..5422778d4a 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -12,7 +12,4 @@ RSpec.configure do |config|
 
   # Fix encoding issue in Rails 5.0; allows passing empty arrays or hashes as params.
   config.before(:each, type: :controller) { @request.env["CONTENT_TYPE"] = 'application/json' }
-
-  # You can use `rspec -n` to run only failed specs.
-  config.example_status_persistence_file_path = "tmp/rspec-status.txt"
 end
diff --git a/spec/support/localized_number_helper.rb b/spec/support/localized_number_helper.rb
index 62ed435de0..75e8803915 100644
--- a/spec/support/localized_number_helper.rb
+++ b/spec/support/localized_number_helper.rb
@@ -21,3 +21,24 @@ shared_examples "a model using the LocalizedNumber module" do |attributes|
     end
   end
 end
+
+shared_examples "a Spree Calculator model using the LocalizedNumber module" do |attributes|
+  before do
+    allow(Spree::Config).to receive(:enable_localized_number?).and_return true
+  end
+
+  attributes.each do |attribute|
+    setter = "#{attribute}="
+
+    it do
+      should_not validate_numericality_of(attribute).
+        with_message(I18n.t('activerecord.errors.messages.calculator_preferred_value_error'))
+    end
+
+    it "does not modify the attribute value when it is invalid" do
+      subject.send(setter, 'invalid')
+      subject.valid?
+      expect(subject.send(attribute)).to eq 'invalid'
+    end
+  end
+end
diff --git a/spec/system/admin/payment_method_spec.rb b/spec/system/admin/payment_method_spec.rb
index c6937a0327..e6de2bca7e 100644
--- a/spec/system/admin/payment_method_spec.rb
+++ b/spec/system/admin/payment_method_spec.rb
@@ -112,6 +112,45 @@ describe '
       expect(page).to have_field "payment_method_distributor_ids_#{@distributors[2].id}",
                                  checked: false
     end
+
+    it "retains and displays data that was just submitted" do
+      login_as_admin
+      visit spree.edit_admin_general_settings_path
+      click_link 'Payment Methods'
+      click_link 'New Payment Method'
+
+      fill_in "payment_method_name", with: 'Cheque payment method'
+      fill_in "payment_method_description", with: "Payment description"
+      select2_select "PayPal Express", from: "payment_method_type"
+      select2_select "Flat Percent", from: 'calc_type'
+
+      click_button 'Create'
+
+      expect(page).to have_field "payment_method_name", with: "Cheque payment method"
+      expect(page).to have_field "payment_method_description", with: "Payment description"
+      expect(page).to have_select("payment_method_type", selected: "PayPal Express")
+      expect(page).to have_select("calc_type", selected: "Flat Percent")
+
+      select2_select "Price Sack", from: 'calc_type'
+
+      click_button 'Create'
+
+      expect(page).to have_select("calc_type", selected: "Price Sack")
+      expect(page).to have_field "payment_method_name", with: "Cheque payment method"
+      expect(page).to have_field "payment_method_description", with: "Payment description"
+      expect(page).to have_select("payment_method_type", selected: "PayPal Express")
+
+      check "payment_method_distributor_ids_#{@distributors[0].id}"
+
+      click_button 'Create'
+
+      expect(page).to have_field "payment_method_distributor_ids_#{@distributors[0].id}",
+                                 checked: true
+      expect(page).to have_select("calc_type", selected: "Price Sack")
+      expect(page).to have_field "payment_method_name", with: "Cheque payment method"
+      expect(page).to have_field "payment_method_description", with: "Payment description"
+      expect(page).to have_select("payment_method_type", selected: "PayPal Express")
+    end
   end
 
   it "updating a payment method" do
@@ -345,4 +384,134 @@ describe '
       end
     end
   end
+
+  context "when updating a payment method with invalid data" do
+    let(:payment_method) { create(:payment_method, :flat_rate, amount: 10) }
+
+    # Persist preferences to test that when preferred values are not found in the cache,
+    # they are fetched from the database and displayed correctly
+    before do
+      Spree::Preferences::Store.instance.persistence = true
+      login_as_admin
+      visit spree.edit_admin_payment_method_path payment_method
+      fill_in "payment_method_name", with: ""
+      fill_in "payment_method_description", with: "Edited description"
+      uncheck "payment_method_distributor_ids_#{@distributors[0].id}"
+      # Although text is not permitted by input[type=number], let's see what happens
+      fill_in "Amount", with: 'invalid'
+      click_button 'Update'
+    end
+
+    after do
+      Spree::Preferences::Store.instance.persistence = false
+    end
+
+    it "displays error details" do
+      expect(page).to have_content("2 errors")
+
+      expect(page).to have_content("Name can't be blank")
+      expect(page).to have_content("At least one hub must be selected")
+
+      # Highlighting invalid fields
+      within '.field_with_errors:has(#payment_method_name)' do
+        expect(page).to have_field "payment_method_name"
+      end
+
+      within '#hubs' do
+        expect(page).to have_selector(".red")
+      end
+    end
+
+    it "keeps information that was just edited, even after multiple unsuccessful updates" do
+      expect(page).to have_field "payment_method_name", with: ''
+      expect(page).to have_field "payment_method_description", with: "Edited description"
+      expect(page).to have_unchecked_field "payment_method_distributor_ids_#{@distributors[0].id}"
+
+      fill_in "payment_method_name", with: "Test name"
+      fill_in "Amount", with: 'invalid string'
+      click_button 'Update'
+
+      expect(page).to have_field "payment_method_name", with: 'Test name'
+      expect(page).to have_field "payment_method_description", with: "Edited description"
+      expect(page).to have_unchecked_field "payment_method_distributor_ids_#{@distributors[0].id}"
+    end
+
+    it 'displays data fetched from the database after navigating away from the page' do
+      click_link 'Back To Payment Methods List'
+      click_link href: /#{spree.edit_admin_payment_method_path(payment_method)}/
+
+      expect(page).to have_field 'Amount', with: '10.0'
+      expect(page).not_to have_field 'payment_method_name', with: ''
+      expect(page).not_to have_field 'payment_method_description', with: 'Edited description'
+      expect(page).to have_checked_field "payment_method_distributor_ids_#{@distributors[0].id}"
+    end
+  end
+
+  context 'when updating payment method with invalid data and changing calculator type' do
+    let(:payment_method) { create(:payment_method, :flat_rate, amount: 10) }
+
+    # Persist preferences to test that when preferred values are not found in the cache,
+    # they are fetched from the database and displayed correctly
+    before do
+      Spree::Preferences::Store.instance.persistence = true
+      login_as_admin
+      visit spree.edit_admin_payment_method_path payment_method
+      fill_in 'payment_method_name', with: ''
+      fill_in 'payment_method_description', with: 'Edited description'
+      uncheck "payment_method_distributor_ids_#{@distributors[0].id}"
+      select2_select 'Flat Percent', from: 'calc_type'
+      click_button 'Update'
+    end
+
+    after do
+      Spree::Preferences::Store.instance.persistence = false
+    end
+
+    it 'displays the number of errors' do
+      expect(page).to have_content('2 errors')
+    end
+
+    it 'displays error messages' do
+      expect(page).to have_content("Name can't be blank")
+      expect(page).to have_content('At least one hub must be selected')
+    end
+
+    it 'displays the new calculator fields' do
+      expect(page).to have_field 'Flat Percent'
+    end
+
+    it 'highlights invalid fields' do
+      within '.field_with_errors:has(#payment_method_name)' do
+        expect(page).to have_field 'payment_method_name'
+      end
+
+      within '#hubs' do
+        expect(page).to have_selector('.red')
+      end
+    end
+
+    it 'keeps information that was just edited, even after multiple unsuccessful updates' do
+      expect(page).to have_field 'payment_method_name', with: ''
+      expect(page).to have_field 'payment_method_description', with: 'Edited description'
+      expect(page).to have_unchecked_field "payment_method_distributor_ids_#{@distributors[0].id}"
+
+      fill_in 'payment_method_name', with: 'Test name'
+      fill_in 'Flat Percent', with: 'invalid string'
+      click_button 'Update'
+
+      expect(page).to have_field 'payment_method_name', with: 'Test name'
+      expect(page).to have_field 'payment_method_description', with: 'Edited description'
+      expect(page).to have_unchecked_field "payment_method_distributor_ids_#{@distributors[0].id}"
+    end
+
+    it 'displays data fetched from the database after navigating away from the page' do
+      click_link 'Back To Payment Methods List'
+      click_link href: /#{spree.edit_admin_payment_method_path(payment_method)}/
+
+      expect(page).to have_field 'Amount', with: '10.0'
+      expect(page).not_to have_field 'payment_method_name', with: ''
+      expect(page).not_to have_field 'payment_method_description', with: 'Edited description'
+      expect(page).to have_checked_field "payment_method_distributor_ids_#{@distributors[0].id}"
+    end
+  end
 end