diff --git a/lib/plugins/acts_as_customizable/lib/acts_as_customizable.rb b/lib/plugins/acts_as_customizable/lib/acts_as_customizable.rb
index 5dcc97dc60..80e001995b 100644
--- a/lib/plugins/acts_as_customizable/lib/acts_as_customizable.rb
+++ b/lib/plugins/acts_as_customizable/lib/acts_as_customizable.rb
@@ -47,7 +47,7 @@ module Redmine
                                    dependent: :delete_all,
                                    validate: false
           before_validation { |customized| customized.custom_field_values if customized.new_record? }
-          validate :validate_custom_values, if: -> (customized) { customized.custom_field_values_changed? }
+          validate :validate_custom_values
           send :include, Redmine::Acts::Customizable::InstanceMethods
           # Save custom values when saving the customized object
           after_save :save_custom_field_values
diff --git a/test/unit/time_entry_activity_test.rb b/test/unit/time_entry_activity_test.rb
index 1d56cdf7e7..07350b4711 100644
--- a/test/unit/time_entry_activity_test.rb
+++ b/test/unit/time_entry_activity_test.rb
@@ -62,7 +62,8 @@ class TimeEntryActivityTest < ActiveSupport::TestCase
 
     e = TimeEntryActivity.new(name: 'Custom Data')
     assert !e.save
-    assert_include e.errors[:custom_values], I18n.translate('activerecord.errors.messages.invalid')
+    assert_include e.errors["custom_field_#{field.id}"],
+                   I18n.translate('activerecord.errors.messages.blank')
   end
 
   def test_create_with_required_custom_field_should_succeed
@@ -85,7 +86,7 @@ class TimeEntryActivityTest < ActiveSupport::TestCase
     # Blanking custom field, save should fail
     e.custom_field_values = { field.id => '' }
     assert !e.save
-    refute_empty e.errors[:custom_values]
+    refute_empty e.errors["custom_field_#{field.id}"]
 
     # Update custom field to valid value, save should succeed
     e.custom_field_values = { field.id => '0' }