diff --git a/library/Director/CustomVariable/CustomVariables.php b/library/Director/CustomVariable/CustomVariables.php
index 01227c597..e8a464983 100644
--- a/library/Director/CustomVariable/CustomVariables.php
+++ b/library/Director/CustomVariable/CustomVariables.php
@@ -399,10 +399,9 @@ 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 a79bf3c79..32e8cf7bc 100644
--- a/library/Director/IcingaConfig/IcingaConfig.php
+++ b/library/Director/IcingaConfig/IcingaConfig.php
@@ -553,6 +553,20 @@ protected function renderHostOverridableVars()
       )
     }
   }
+  globals.directorMergeOverrideConfig = function(existing,overrides) {
+    if (existing) {
+      for (service => conf in overrides) {
+        if (existing[service]) {
+          existing[service] += conf
+        } else {
+          existing[service] = conf
+        }
+      }
+      return existing
+    } else {
+      return overrides
+    }
+  }
 
   template Service DirectorOverrideTemplate {
     /**