--- modules/system/system.css
+++ modules/system/system.css
@@ -133,6 +133,12 @@
 .form-item input.error, .form-item textarea.error, .form-item select.error {
   border: 2px solid red;
 }
+
+.form-item input[type="checkbox"].error, .form-item input[type="radio"].error{
+  outline: 2px solid red;
+  -moz-appearance: none;
+}
+
 .form-item .description {
   font-size: 0.85em;
 }