diff --git a/relation_ui.module b/relation_ui.module
index b2d018e..0702b31 100644
--- a/relation_ui.module
+++ b/relation_ui.module
@@ -347,6 +347,15 @@ function relation_ui_type_form($form, &$form_state, $relation_type = array(), $o
 }
 
 /**
+ * Validate relation type form.
+ */
+function relation_ui_type_form_validate($form, &$form_state) {
+  if ($form_state['values']['advanced']['min_arity'] > $form_state['values']['advanced']['max_arity']) {
+    form_set_error('min_arity', t('Min arity must be less or equal to max arity'));
+  }
+}
+
+/**
  * Submit data from bundle settings page.
  */
 function relation_ui_type_form_submit($form, &$form_state) {