diff --git a/library/Icinga/Web/Url.php b/library/Icinga/Web/Url.php
index 3f94a0410..2006cb180 100644
--- a/library/Icinga/Web/Url.php
+++ b/library/Icinga/Web/Url.php
@@ -174,7 +174,7 @@ class Url
         }
         // TODO: This has been used by former filter implementation, remove it:
         if (isset($urlParts['query'])) {
-            $params = UrlParams::fromQueryString($urlParts['query'])->addValues($params);
+            $params = UrlParams::fromQueryString($urlParts['query'])->mergeValues($params);
         }
 
         $fragment = self::getUrlFragment($url);
@@ -381,8 +381,9 @@ class Url
             }
             $this->params = $urlParams;
         } else {
-            // TODO: ProgrammingError?
-            throw new \Exception('Url, params, WTF');
+            throw new ProgrammingError(
+                'Url params needs to be either an array or an UrlParams instance'
+            );
         }
         return $this;
     }
diff --git a/library/Icinga/Web/UrlParams.php b/library/Icinga/Web/UrlParams.php
index a9d0eb79a..ecb9c5230 100644
--- a/library/Icinga/Web/UrlParams.php
+++ b/library/Icinga/Web/UrlParams.php
@@ -156,6 +156,33 @@ class UrlParams
         return $this;
     }
 
+    protected function clearValues()
+    {
+        $this->params = array();
+        $this->index = array();
+    }
+
+    public function mergeValues($param, $values = null)
+    {
+        if ($values === null && is_array($param)) {
+            foreach ($param as $k => $v) {
+                $this->set($k, $v);
+            }
+        } else {
+            foreach ($values as $value) {
+                $this->set($param, $value);
+            }
+        }
+
+        return $this;
+    }
+
+    public function setValues($param, $values = null)
+    {
+        $this->clearValues();
+        return $this->addValues($param, $values);
+    }
+
     /**
      * Add the given parameter with the given value in front of all other values
      *