diff --git a/app/services/product_service.rb b/app/services/product_service.rb
index d88169ab1..1bd34d137 100644
--- a/app/services/product_service.rb
+++ b/app/services/product_service.rb
@@ -25,7 +25,7 @@ class ProductService
     end
 
     # amount params multiplied by hundred
-    def self.amount_multiplied_by_hundred(amount)
+    def amount_multiplied_by_hundred(amount)
       if amount.present?
         v = amount.to_f