diff --git a/modules/file/file.js b/modules/file/file.js
index 937c543..996240e 100644
--- a/modules/file/file.js
+++ b/modules/file/file.js
@@ -17,7 +17,7 @@ Drupal.behaviors.fileValidateAutoAttach = {
     if (settings.file && settings.file.elements) {
       $.each(settings.file.elements, function(selector) {
         var extensions = settings.file.elements[selector];
-        $(selector, context).once(function() {
+        $(selector, context).once('file-validation-extension', function() {
           $(this).bind('change', {extensions: extensions}, Drupal.file.validateExtension);
         });
       });
@@ -27,6 +27,7 @@ Drupal.behaviors.fileValidateAutoAttach = {
     if (settings.file && settings.file.elements) {
       $.each(settings.file.elements, function(selector) {
         $(selector, context).unbind('change', Drupal.file.validateExtension);
+        $(selector, context).removeClass('field-validation-extension-processed');
       });
     }
   }