diff --git a/misc/ajax.js b/misc/ajax.js
index bb4a6e1..1cb6253 100644
--- a/misc/ajax.js
+++ b/misc/ajax.js
@@ -432,8 +432,8 @@ Drupal.ajax.prototype.success = function (response, status) {
   // Reattach behaviors, if they were detached in beforeSerialize(). The
   // attachBehaviors() called on the new content from processing the response
   // commands is not sufficient, because behaviors from the entire form need
-  // to be reattached.
-  if (this.form) {
+  // to be reattached, if it's still part of the document.
+  if (this.form && $.contains(document, this.form.get(0))) {
     var settings = this.settings || Drupal.settings;
     Drupal.attachBehaviors(this.form, settings);
   }
@@ -488,8 +488,9 @@ Drupal.ajax.prototype.error = function (xmlhttprequest, uri, customMessage) {
   $(this.wrapper).show();
   // Re-enable the element.
   $(this.element).removeClass('progress-disabled').removeAttr('disabled');
-  // Reattach behaviors, if they were detached in beforeSerialize().
-  if (this.form) {
+  // Reattach behaviors, if they were detached in beforeSerialize(), and the
+  // form is still part of the document.
+  if (this.form && $.contains(document, this.form.get(0))) {
     var settings = this.settings || Drupal.settings;
     Drupal.attachBehaviors(this.form, settings);
   }