diff --git a/library/Icinga/File/Ini/IniWriter.php b/library/Icinga/File/Ini/IniWriter.php
index 1f470b006a..2131bc8825 100644
--- a/library/Icinga/File/Ini/IniWriter.php
+++ b/library/Icinga/File/Ini/IniWriter.php
@@ -69,7 +69,7 @@ public function __construct(Config $config, $filename, $filemode = 0660, $option
      */
     public function render()
     {
-        if (file_exists($this->filename)) {
+        if ($this->filename !== null && file_exists($this->filename)) {
             $oldconfig = Config::fromIni($this->filename);
             $content = trim(file_get_contents($this->filename));
         } else {