diff --git a/core/modules/field/field.attach.inc b/core/modules/field/field.attach.inc
index 4d8fdad..6fdace0 100644
--- a/core/modules/field/field.attach.inc
+++ b/core/modules/field/field.attach.inc
@@ -189,6 +189,8 @@ function _field_invoke($op, $entity_type, $entity, &$a = NULL, &$b = NULL, $opti
   // Iterate through the instances and collect results.
   $return = array();
   foreach ($instances as $instance) {
+    // field_info_field() is not available for deleted fields, so use
+    // field_info_field_by_id().
     $field = field_info_field_by_id($instance['field_id']);
     $field_name = $field['field_name'];
     $function = $options['default'] ? 'field_default_' . $op : $field['module'] . '_field_' . $op;