diff --git a/.horde.yml b/.horde.yml
index 8b5414d..e03fabf 100644
--- a/.horde.yml
+++ b/.horde.yml
@@ -48,7 +48,7 @@ dependencies:
       horde/core: ^3
       horde/exception: ^3
       horde/group: ^3
-      horde/form: ^3
+      horde/form: ^3.1
       horde/imap_client: ^3
       horde/managesieve: ^2
       horde/mime: ^3
diff --git a/composer.json b/composer.json
index d175d91..8a99909 100644
--- a/composer.json
+++ b/composer.json
@@ -37,7 +37,7 @@
         "horde/core": "^3 || dev-FRAMEWORK_6_0",
         "horde/exception": "^3 || dev-FRAMEWORK_6_0",
         "horde/group": "^3 || dev-FRAMEWORK_6_0",
-        "horde/form": "^3 || dev-FRAMEWORK_6_0",
+        "horde/form": "^3.1 || dev-FRAMEWORK_6_0",
         "horde/imap_client": "^3 || dev-FRAMEWORK_6_0",
         "horde/managesieve": "^2 || dev-FRAMEWORK_6_0",
         "horde/mime": "^3 || dev-FRAMEWORK_6_0",
diff --git a/lib/Form/Forward.php b/lib/Form/Forward.php
index 01cbe3c..680b8f2 100644
--- a/lib/Form/Forward.php
+++ b/lib/Form/Forward.php
@@ -28,7 +28,7 @@ public function __construct($vars, $title = '', $name = null)
 
         $v = $this->addVariable(_("Keep a copy of messages in this account?"), 'keep_copy', 'boolean', false);
         $v->setHelp('forward-keepcopy');
-        $v = $this->addVariable(_("Address(es) to forward to:"), 'addresses', 'ingo:Longemail', false, false, null, [5, 40]);
+        $v = $this->addVariable(_("Address(es) to forward to:"), 'addresses', \Horde\Ingo\Form\V3\LongemailVariable::class, false, false, null, [5, 40]);
         $v->setHelp('forward-addresses');
         $this->setButtons(_("Save"));
     }
diff --git a/lib/Form/Spam.php b/lib/Form/Spam.php
index 416830f..9d72b93 100644
--- a/lib/Form/Spam.php
+++ b/lib/Form/Spam.php
@@ -50,7 +50,7 @@ public function __construct($vars, $title = '', $name = null)
         $this->folder_var = $this->addVariable(
             _("Folder to receive spam:"),
             'folder',
-            'ingo:folders',
+            \Horde\Ingo\Form\V3\FoldersVariable::class,
             true
         );
         $this->folder_var->setHelp('spam-folder');
diff --git a/lib/Form/Vacation.php b/lib/Form/Vacation.php
index b2a3770..dca53c5 100644
--- a/lib/Form/Vacation.php
+++ b/lib/Form/Vacation.php
@@ -72,11 +72,11 @@ public function __construct($vars, $title = '', $name = null, $features = null)
             || $this->hasFeature('days')) {
             $this->setSection('advanced', _("Advanced Settings"));
             if ($this->hasFeature('addresses')) {
-                $v = $this->addVariable(_("My email addresses:"), 'addresses', 'ingo:Longemail', true, false, null, [5, 40]);
+                $v = $this->addVariable(_("My email addresses:"), 'addresses', \Horde\Ingo\Form\V3\LongemailVariable::class, true, false, null, [5, 40]);
                 $v->setHelp('vacation-myemail');
             }
             if ($this->hasFeature('excludes')) {
-                $v = $this->addVariable(_("Addresses to not send responses to:"), 'excludes', 'ingo:Longemail', false, false, null, [10, 40]);
+                $v = $this->addVariable(_("Addresses to not send responses to:"), 'excludes', \Horde\Ingo\Form\V3\LongemailVariable::class, false, false, null, [10, 40]);
                 $v->setHelp('vacation-noresponse');
             }
             if ($this->hasFeature('ignorelist')) {
diff --git a/src/Form/V3/FoldersVariable.php b/src/Form/V3/FoldersVariable.php
index 45166cb..13aaf44 100644
--- a/src/Form/V3/FoldersVariable.php
+++ b/src/Form/V3/FoldersVariable.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Ingo\Form\V3;
+namespace Horde\Ingo\Form\V3;
 
 use Horde\Util\Variables;
 use Horde\Form\V3\BaseVariable;
@@ -30,6 +30,16 @@ class FoldersVariable extends BaseVariable
     public $_folder;
     public $newFolderSet;
 
+    /**
+     * Return the legacy type name so Ingo_Ui_VarRenderer_Html's
+     * _renderVarInput_ingo_form_type_folders() is still dispatched to after
+     * the class was moved from Ingo\Form\V3 to Horde\Ingo\Form\V3.
+     */
+    public function getTypeName(): string
+    {
+        return 'ingo_form_type_folders';
+    }
+
     public function isValid(Horde_Variables|Variables $vars, $value): bool
     {
         if ($this->newFolderSet || strlen($value)) {
diff --git a/src/Form/V3/LongemailVariable.php b/src/Form/V3/LongemailVariable.php
index 40d43c3..fdc3967 100644
--- a/src/Form/V3/LongemailVariable.php
+++ b/src/Form/V3/LongemailVariable.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Ingo\Form\V3;
+namespace Horde\Ingo\Form\V3;
 
 use Horde\Util\Variables;
 use Horde\Form\V3\LongtextVariable;
@@ -30,6 +30,16 @@
  */
 class LongemailVariable extends LongtextVariable
 {
+    /**
+     * Return the legacy type name so Ingo_Ui_VarRenderer_Html's
+     * _renderVarInput_ingo_form_type_longemail() is still dispatched to after
+     * the class was moved from Ingo\Form\V3 to Horde\Ingo\Form\V3.
+     */
+    public function getTypeName(): string
+    {
+        return 'ingo_form_type_longemail';
+    }
+
     /**
      */
     public function isValid(Horde_Variables|Variables $vars, $value): bool