diff --git a/authcache.formtokenids.js b/authcache.formtokenids.js
index 0fe22a5..8dab6c2 100644
--- a/authcache.formtokenids.js
+++ b/authcache.formtokenids.js
@@ -20,4 +20,26 @@
       });
     }
   };
+
+  Drupal.behaviors.authcacheFormBuildId = {
+    attach: function (context, settings) {
+      if ($.isEmptyObject(settings.authcacheFormTokenIds)) {
+        return;
+      }
+
+      // Retrieve new build id using an AJAX command.
+      $.AuthcacheAjax.cmd('form_build_id', settings.authcacheFormBuildIds, function(evt, result) {
+        if ($.isEmptyObject(result)) {
+          return;
+        }
+
+        // Inject the hidden form_build_id input after each hidden form_id input.
+        $("form input[name='form_id']", context).once('authcacheFormBuildIds').after(function() {
+          if (settings.authcacheFormBuildIds[this.value] && result[this.value]) {
+            return "<input type='hidden' name='form_build_id' value='" + result[this.value] + "'/>"
+          }
+        });
+      });
+    }
+  };
 }(jQuery));
diff --git a/authcache.info b/authcache.info
index 2ea5296..7695546 100644
--- a/authcache.info
+++ b/authcache.info
@@ -4,4 +4,5 @@ package = Performance and scalability
 core = 7.x
 configure = admin/config/system/authcache
 files[] = includes/AuthcacheFormTokenIdCommand.inc
+files[] = includes/AuthcacheFormBuildIdCommand.inc
 files[] = includes/AuthcacheMenuLocalTasksCommand.inc
diff --git a/authcache.module b/authcache.module
index e1bd60b..ad3872f 100644
--- a/authcache.module
+++ b/authcache.module
@@ -203,6 +203,8 @@ function authcache_form_alter(&$form, &$form_state, $form_id) {
  * @see drupal_build_form().
  */
 function _authcache_form_after_build($form, $form_state) {
+  global $user;
+
   $form_id = $form['#form_id'];
 
   if (isset($form['form_token']) && !authcache_get_request_property('ajax')) {
@@ -215,6 +217,23 @@ function _authcache_form_after_build($form, $form_state) {
       unset($form['form_build_id']);
       unset($form['#build_id']);
     }
+    elseif ($user->uid) {
+      // Remove the build-id hidden field
+      unset($form['form_build_id']);
+
+      // Otherwise store prototype-form builds in the cache for authenticated
+      // users.
+      drupal_add_js(drupal_get_path('module', 'authcache') . '/authcache.formtokenids.js');
+      drupal_add_js(array('authcacheFormBuildIds' => array(
+        $form_id => $form['#build_id'],
+      )), 'setting');
+      authcache_ajax_add_command('form_build_id');
+
+      // Prepend 'authcache-' to the build-id. Those builds will serve as
+      // prototypes when generating new forms for other users from within
+      // AuthcacheFormBuildIdCommand.
+      $form['#build_id'] = 'authcache-' . $form['#build_id'];
+    }
 
     if (isset($form['form_token']) && authcache_get_request_property('ajax')) {
       // Remove CSRF-token from built form and make sure it can be retrieved
@@ -1265,6 +1284,13 @@ function authcache_authcache_ajax_command() {
         'maxage' => ini_get('session.cookie_lifetime') ?: 0,
       ),
     ),
+    'form_build_id' => array(
+      'handler' => 'AuthcacheFormBuildIdCommand',
+      'request' => 'formbuild',
+      'request config' => array(
+        'maxage' => 21600,
+      ),
+    ),
     'menu_local_tasks' => array(
       'handler' => 'AuthcacheMenuLocalTasksCommand',
       'handler config' => array(
diff --git a/includes/AuthcacheFormBuildIdCommand.inc b/includes/AuthcacheFormBuildIdCommand.inc
new file mode 100644
index 0000000..5f922a2
--- /dev/null
+++ b/includes/AuthcacheFormBuildIdCommand.inc
@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * Generate new per-user form-cache entries by copying them from prototypes.
+ *
+ * @see form.inc
+ */
+class AuthcacheFormBuildIdCommand extends AuthcacheAjaxCommandHandlerBase {
+  public function run($op, $forms) {
+    include_once DRUPAL_ROOT . '/includes/common.inc';
+    include_once DRUPAL_ROOT . '/includes/form.inc';
+
+    foreach ($forms as $form_id => $form_build_id) {
+      // Retrieve prototype from form cache. Authcache prototype forms are
+      // prefixed with "form_authcache-".
+      if ($cached = cache_get('form_authcache-' . $form_build_id, 'cache_form')) {
+        $form = $cached->data;
+
+        global $user;
+        if ($form['#form_id'] == $form_id) {
+          if ($cached = cache_get('form_state_authcache-' . $form_build_id, 'cache_form')) {
+            $form_state = $cached->data;
+
+            $new_build_id = 'form-' . drupal_hash_base64(uniqid(mt_rand(), TRUE) . mt_rand());
+            $form['#build_id'] = $new_build_id;
+            $form['form_build_id']['#value'] = $new_build_id;
+            $form['form_build_id']['#id'] = $new_build_id;
+
+            // Store new form for the current user in the form cache. Note that
+            // form_set_cache will replace the per-user #cache_token before
+            // storing it.
+            form_set_cache($new_build_id, $form, $form_state);
+
+            // Report the new build-id back to the browser
+            $buildids[$form_id] = $new_build_id;
+          }
+        }
+      }
+    }
+
+    return $buildids;
+  }
+}