diff --git a/app/controllers/epp/domains_controller.rb b/app/controllers/epp/domains_controller.rb
index 82eae2105..5fe1df879 100644
--- a/app/controllers/epp/domains_controller.rb
+++ b/app/controllers/epp/domains_controller.rb
@@ -127,45 +127,46 @@ class Epp::DomainsController < EppController
 
   def validate_create
     @prefix = 'create > create >'
-    requires('name', 'ns', 'registrant', 'ns > hostAttr')
+    requires 'name', 'ns', 'registrant', 'ns > hostAttr'
 
     @prefix = 'extension > create >'
     mutually_exclusive 'keyData', 'dsData'
 
     @prefix = nil
-    requires('extension > extdata > legalDocument')
+    requires 'extension > extdata > legalDocument'
   end
 
   def validate_renew
     @prefix = 'renew > renew >'
-    requires('name', 'curExpDate', 'period')
+    requires 'name', 'curExpDate', 'period'
   end
 
   def validate_update
     if element_count('update > chg > registrant') > 0
-      requires('extension > extdata > legalDocument')
+      requires 'extension > extdata > legalDocument'
     end
 
     @prefix = 'update > update >'
-    requires('name')
+    requires 'name'
   end
 
   ## TRANSFER
   def validate_transfer
-    @prefix = 'transfer > transfer >'
-    requires('name')
+    requires 'transfer > transfer'
 
-    op = params[:parsed_frame].css('transfer').first[:op]
-    return if %w(approve query reject).include?(op)
-    epp_errors << { code: '2306', msg: I18n.t('errors.messages.attribute_op_is_invalid') }
+    @prefix = 'transfer > transfer >'
+    requires 'name'
+
+    @prefix = nil
+    requires_attribute 'transfer', 'op', values: %(approve, query, reject)
   end
 
   ## DELETE
   def validate_delete
-    requires('extension > extdata > legalDocument')
+    requires 'extension > extdata > legalDocument'
 
     @prefix = 'delete > delete >'
-    requires('name')
+    requires 'name'
   end
 
   def domain_create_params
diff --git a/app/controllers/epp_controller.rb b/app/controllers/epp_controller.rb
index 8981dcd8f..cf18f211d 100644
--- a/app/controllers/epp_controller.rb
+++ b/app/controllers/epp_controller.rb
@@ -62,20 +62,56 @@ class EppController < ApplicationController
     handle_errors and return if epp_errors.any?
   end
 
+  # let's follow grape's validations: https://github.com/intridea/grape/#parameter-validation-and-coercion
+
+  # Example usage:
+  #
+  #    requires 'transfer'
+  #
+  # Adds error to epp_errors if element is missing or blank
+  # Returns last element of selectors if it exists
+  #
+  # TODO: Add possibility to pass validations / options in the method
+
   def requires(*selectors)
+    el, missing = nil, nil
     selectors.each do |selector|
       full_selector = [@prefix, selector].join(' ')
       el = params[:parsed_frame].css(full_selector).first
+
+      missing = el.nil? || (el.text.blank? && el.children.none?)
+
       epp_errors << {
         code: '2003',
         msg: I18n.t('errors.messages.required_parameter_missing', key: el.try(:name) || selector)
-      } if el.nil? || el.text.blank?
+      } if missing
     end
 
-    epp_errors.empty?
+    missing ? false : el # return last selector if it was present
+  end
+
+  # Example usage:
+  #
+  #    requires_attribute 'transfer', 'op', values: %(approve, query, reject)
+  #
+  # Adds error to epp_errors if element or attribute is missing or attribute attribute is not one
+  # of the values
+
+  def requires_attribute(element_selector, attribute_selector, options)
+    element = requires(element_selector)
+    return unless element
+
+    attribute = element[attribute_selector]
+
+    values = options.delete(:values)
+    return if attribute && values.include?(attribute)
+
+    epp_errors << {
+      code: '2306',
+      msg: I18n.t('attribute_is_invalid', attribute: attribute_selector)
+    }
   end
 
-  # let's follow grape's validations: https://github.com/intridea/grape/#parameter-validation-and-coercion
   def exactly_one_of(*selectors)
     return if element_count(*selectors) == 1
 
diff --git a/config/locales/en.yml b/config/locales/en.yml
index b14579991..a6e4c18ed 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -269,7 +269,6 @@ en:
       invalid_type: 'PostalInfo type is invalid'
       unimplemented_command: 'Unimplemented command'
       domain_exists_but_belongs_to_other_registrar: 'Domain exists but belongs to other registrar'
-      attribute_op_is_invalid: 'Attribute op is invalid'
 
 
   code: 'Code'
@@ -501,3 +500,4 @@ en:
   unknown_expiry_relative_pattern: 'Expiry relative must be compatible to ISO 8601'
   unknown_expiry_absolute_pattern: 'Expiry absolute must be compatible to ISO 8601'
   mutally_exclusive_params: 'Mutually exclusive parameters: %{params}'
+  attribute_is_invalid: 'Attribute is invalid: %{attribute}'
diff --git a/spec/epp/domain_spec.rb b/spec/epp/domain_spec.rb
index 355c06f09..5fe84c283 100644
--- a/spec/epp/domain_spec.rb
+++ b/spec/epp/domain_spec.rb
@@ -944,7 +944,7 @@ describe 'EPP Domain', epp: true do
     it 'returns an error for incorrect op attribute' do
       response = epp_plain_request(domain_transfer_xml({}, 'bla'), :xml)
       response[:result_code].should == '2306'
-      response[:msg].should == 'Attribute op is invalid'
+      response[:msg].should == 'Attribute is invalid: op'
     end
 
     it 'creates new pw after successful transfer' do