diff --git a/test/unit/custom_field_test.rb b/test/unit/custom_field_test.rb
index a6e7d8e..580e268 100644
--- a/test/unit/custom_field_test.rb
+++ b/test/unit/custom_field_test.rb
@@ -28,8 +28,8 @@ class CustomFieldTest < ActiveSupport::TestCase
   def test_regexp_validation
     field = IssueCustomField.new(:name => 'regexp', :field_format => 'text', :regexp => '[a-z0-9')
     assert !field.save
-    assert_equal I18n.t('activerecord.errors.messages.invalid'), field.errors.on(:regexp)
-
+    assert_equal I18n.t('activerecord.errors.messages.invalid'),
+                 field.errors[:regexp].to_s
     field.regexp = '[a-z0-9]'
     assert field.save
   end