diff --git a/wcfsetup/install/files/lib/system/image/adapter/ImagickImageAdapter.class.php b/wcfsetup/install/files/lib/system/image/adapter/ImagickImageAdapter.class.php
index f2e9d0d2d62..e414f312dc0 100644
--- a/wcfsetup/install/files/lib/system/image/adapter/ImagickImageAdapter.class.php
+++ b/wcfsetup/install/files/lib/system/image/adapter/ImagickImageAdapter.class.php
@@ -125,6 +125,9 @@ public function createEmptyImage($width, $height)
      */
     public function createThumbnail($maxWidth, $maxHeight, $preserveAspectRatio = true)
     {
+        $maxHeight = (int)$maxHeight;
+        $maxWidth = (int)$maxWidth;
+
         $thumbnail = clone $this->imagick;
 
         if ($thumbnail->getImageFormat() == 'GIF') {