diff --git a/library/Director/CustomVariable/CustomVariables.php b/library/Director/CustomVariable/CustomVariables.php
index 848adb902..fbed9fd56 100644
--- a/library/Director/CustomVariable/CustomVariables.php
+++ b/library/Director/CustomVariable/CustomVariables.php
@@ -393,10 +393,9 @@ public function toLegacyConfigString()
     protected function renderSingleVar($key, $var, $renderExpressions = false)
     {
         if ($key === $this->overrideKeyName) {
-            return c::renderKeyOperatorValue(
+            return c::renderKeyValue(
                 $this->renderKeyName($key),
-                '+=',
-                $var->toConfigStringPrefetchable($renderExpressions)
+                'directorMergeOverrideConfig('.$this->renderKeyName($key) . ', ' . $var->toConfigStringPrefetchable($renderExpressions).')'
             );
         } else {
             return c::renderKeyValue(
diff --git a/library/Director/IcingaConfig/IcingaConfig.php b/library/Director/IcingaConfig/IcingaConfig.php
index 72edd7eeb..24cbb1df9 100644
--- a/library/Director/IcingaConfig/IcingaConfig.php
+++ b/library/Director/IcingaConfig/IcingaConfig.php
@@ -540,6 +540,20 @@ protected function renderHostOverridableVars()
       )
     }
   }
+  globals.directorMergeOverrideConfig = function(existing,overrides) {
+    if (existing) {
+      for (var service => conf in overrides) {
+        if (existing[service]) {
+          existing[service] += conf
+        } else {
+          existing[service] = conf
+        }
+      }
+      return existing
+    } else {
+      return overrides
+    }
+  }
 
   template Service DirectorOverrideTemplate {
     /**