diff --git a/app/controllers/spree/admin/payment_methods_controller.rb b/app/controllers/spree/admin/payment_methods_controller.rb
index 72ac7a7a35..e4d1d8f3ed 100644
--- a/app/controllers/spree/admin/payment_methods_controller.rb
+++ b/app/controllers/spree/admin/payment_methods_controller.rb
@@ -7,6 +7,7 @@ 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_amount, only: [:update]
 
       respond_to :html
 
@@ -173,6 +174,16 @@ module Spree
           params_for_update
         end
       end
+
+      def validate_calculator_preferred_amount
+        preferred_amount = params.dig(:payment_method_check, :calculator_attributes,
+                                      :preferred_amount)
+        return if preferred_amount.nil? || Float(preferred_amount,
+                                                 exception: false)
+
+        flash[:error] = I18n.t(:calculator_preferred_amount_error)
+        redirect_to spree.edit_admin_payment_method_path(@payment_method)
+      end
     end
   end
 end
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 8e3acde16e..9f934a9110 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -2321,6 +2321,7 @@ See the %{link} to find out more about %{sitename}'s features and to start using
   calculator_values: "Calculator values"
   calculator_settings_warning: "If you are changing the calculator type, you must save first before you can edit the calculator settings"
   calculator_preferred_unit_error: "must be kg or lb"
+  calculator_preferred_amount_error: "Invalid input. Please use only numbers. For example: 10, 5.5, -20"
   flat_percent_per_item: "Flat Percent (per item)"
   flat_rate_per_item: "Flat Rate (per item)"
   flat_rate_per_order: "Flat Rate (per order)"