diff --git a/app/controllers/spree/admin/general_settings_controller.rb b/app/controllers/spree/admin/general_settings_controller.rb
index b6714b0660..7c2ef6e695 100644
--- a/app/controllers/spree/admin/general_settings_controller.rb
+++ b/app/controllers/spree/admin/general_settings_controller.rb
@@ -10,7 +10,7 @@ module Spree
       end
 
       def update
-        merge_available_units_params
+        merge_available_units_params unless params[:available_units].nil?
         params.each do |name, value|
           next unless Spree::Config.has_preference? name