diff --git a/library/Director/Objects/IcingaObject.php b/library/Director/Objects/IcingaObject.php
index 1351ca0b..4cd4619e 100644
--- a/library/Director/Objects/IcingaObject.php
+++ b/library/Director/Objects/IcingaObject.php
@@ -290,7 +290,7 @@ abstract class IcingaObject extends DbObject implements IcingaConfigRenderer
         }
 
         if ($this->hasRelation($key)) {
-            if (! $value) {
+            if (strlen($value) === 0) {
                 return parent::set($key . '_id', null);
             }