diff --git a/library/Icinga/Web/Helper/Markdown/LinkTransformer.php b/library/Icinga/Web/Helper/Markdown/LinkTransformer.php
index 4fd69a790..781bd0546 100644
--- a/library/Icinga/Web/Helper/Markdown/LinkTransformer.php
+++ b/library/Icinga/Web/Helper/Markdown/LinkTransformer.php
@@ -5,7 +5,6 @@ namespace Icinga\Web\Helper\Markdown;
 
 use HTMLPurifier_AttrTransform;
 use HTMLPurifier_Config;
-use ipl\Stdlib\Str;
 use ipl\Web\Url;
 
 class LinkTransformer extends HTMLPurifier_AttrTransform
@@ -48,8 +47,12 @@ class LinkTransformer extends HTMLPurifier_AttrTransform
         }
 
         $url = Url::fromPath($attr['href']);
+        $fileName = basename($url->getPath());
 
-        list($_, $ext) = Str::symmetricSplit($url->getPath(), '.', 2);
+        $ext = null;
+        if (($extAt = strrpos($fileName, '.')) !== false) {
+            $ext = substr($fileName, $extAt + 1);
+        }
 
         $hasThumbnail = $ext !== null && in_array($ext, static::$IMAGE_FILES, true);
         $useIframe = $ext !== null && ! in_array($ext, static::$NON_IFRAME_FILES, true);