diff --git a/library/Icinga/Web/Url.php b/library/Icinga/Web/Url.php
index f4fcba381..7b9af3644 100644
--- a/library/Icinga/Web/Url.php
+++ b/library/Icinga/Web/Url.php
@@ -179,10 +179,9 @@ class Url
         }
 
         $urlParts = parse_url($url);
-        if (isset($urlParts['scheme']) && (
-            $urlParts['scheme'] !== $request->getScheme()
+        if ((isset($urlParts['scheme']) && $urlParts['scheme'] !== $request->getScheme())
             || (isset($urlParts['host']) && $urlParts['host'] !== $request->getServer('SERVER_NAME'))
-            || (isset($urlParts['port']) && $urlParts['port'] != $request->getServer('SERVER_PORT')))
+            || (isset($urlParts['port']) && $urlParts['port'] != $request->getServer('SERVER_PORT'))
         ) {
             $urlObject->setIsExternal();
         }
diff --git a/test/php/library/Icinga/Web/UrlTest.php b/test/php/library/Icinga/Web/UrlTest.php
index cbe8b6bf8..6a6088f2f 100644
--- a/test/php/library/Icinga/Web/UrlTest.php
+++ b/test/php/library/Icinga/Web/UrlTest.php
@@ -71,6 +71,11 @@ class UrlTest extends BaseTestCase
         );
     }
 
+    public function testWhetherProtocolRelativeUrlsAreDetectedAsBeingExternal()
+    {
+        $this->assertTrue(Url::fromPath('//testhost/path/to/my/url.html')->isExternal());
+    }
+
     public function testWhetherGetAbsoluteUrlReturnsTheGivenUsernameAndPassword()
     {
         $url = Url::fromPath('http://testusername:testpassword@testsite.com/path/to/my/url.html');