diff --git a/library/Director/Objects/IcingaService.php b/library/Director/Objects/IcingaService.php
index a37080f4..a5f56624 100644
--- a/library/Director/Objects/IcingaService.php
+++ b/library/Director/Objects/IcingaService.php
@@ -218,7 +218,7 @@ class IcingaService extends IcingaObject
             return '';
         }
 
-        if ($this->get('assign_filter')) {
+        if ($this->get('assign_filter') !== null) {
             return $this->renderLegacyResolvedAssignFilter();
         }