diff --git a/modules/file/file.field.inc b/modules/file/file.field.inc
index 59b547a..8263015 100644
--- a/modules/file/file.field.inc
+++ b/modules/file/file.field.inc
@@ -92,6 +92,7 @@ function file_field_instance_settings_form($field, $instance) {
     '#description' => t('Separate extensions with a space or comma and do not include the leading dot.'),
     '#element_validate' => array('_file_generic_settings_extensions'),
     '#weight' => 1,
+    '#maxlength' => 256,
     // By making this field required, we prevent a potential security issue
     // that would allow files of any type to be uploaded.
     '#required' => TRUE,