diff --git a/lib/Horde/Url.php b/lib/Horde/Url.php
index b7099fd..af66173 100644
--- a/lib/Horde/Url.php
+++ b/lib/Horde/Url.php
@@ -265,6 +265,14 @@ public function toString($raw = false, $full = true)
         }
 
         if ($params = $this->parameters) {
+            foreach ($params as $p => &$v) {
+                // TODO: Investigate if it should be done for all (or some) other objects
+                if ($v instanceof Horde_Url) {
+                    $v = strval($v);
+                }
+            }
+            unset($v);
+
             $url .= '?' . http_build_query($params, "", $raw ? '&' : '&');
         }
 
@@ -272,7 +280,7 @@ public function toString($raw = false, $full = true)
             $url .= '#' . ($raw ? $this->anchor : rawurlencode($this->anchor));
         }
 
-        return strval($url);
+        return $url;
     }
 
     /**
@@ -297,7 +305,7 @@ public function __toString()
      */
     public function link(array $attributes = array())
     {
-        $url = (string)$this->setRaw(false);
+        $url = strval($this->setRaw(false));
         $link = '<a';
         if (!empty($url)) {
             $link .= " href=\"$url\"";
diff --git a/test/Horde/Url/AddHordeUrlTest.php b/test/Horde/Url/AddHordeUrlTest.php
new file mode 100644
index 0000000..314dd8c
--- /dev/null
+++ b/test/Horde/Url/AddHordeUrlTest.php
@@ -0,0 +1,23 @@
+<?php
+/**
+ * @author     Dmitry Petrov <dpetrov67@gmail.com>
+ * @license    http://www.horde.org/licenses/lgpl21 LGPL 2.1
+ * @category   Horde
+ * @package    Url
+ * @subpackage UnitTests
+ */
+
+namespace Horde\Url;
+use \PHPUnit\Framework\TestCase;
+use \Horde_Url;
+
+class AddHordeUrlTest extends TestCase
+{
+    public function testAddHordeUrlToExistingUrl()
+    {
+        $url = new Horde_Url('test?foo=1&bar=2');
+        $url->add('url', new Horde_Url('https://example.com/test?_t=123456&_h=Abcd123'));
+        $this->assertEquals('test?foo=1&bar=2&url=https%3A%2F%2Fexample.com%2Ftest%3F_t%3D123456%26_h%3DAbcd123', (string)$url);
+    }
+
+}