diff --git a/core/modules/block/block.admin.inc b/core/modules/block/block.admin.inc
index 2b3c2dd..1c1a2f4 100644
--- a/core/modules/block/block.admin.inc
+++ b/core/modules/block/block.admin.inc
@@ -173,6 +173,16 @@ function block_admin_display_form($form, &$form_state, $blocks, $theme, $block_r
 }
 
 /**
+ * Form element validation handler for block administration form element.
+ */
+function block_admin_display_form_validate($form, &$form_state) {
+  if(isset($form_state['values']['blocks']['system_main']['region']) && $form_state['values']['blocks']['system_main']['region'] == -1) {
+   $message = array('!name' => $form['blocks']['system_main']['region']['#title']);
+   form_set_error('blocks][system_main', t('!name field is required.', $message));
+  }
+}
+
+/**
  * Form submission handler for block_admin_display_form().
  *
  * @see block_admin_display_form()