diff --git a/api/src/Storage.php b/api/src/Storage.php
index 4c011c24f5..d1a30a7821 100644
--- a/api/src/Storage.php
+++ b/api/src/Storage.php
@@ -432,7 +432,7 @@ class Storage extends Storage\Base
 
 		// if no CFs are defined OR used and became unavailable (deleted or permissions changed)
 		if (!$this->customfields && strpos($order_by, self::CF_PREFIX) === false &&
-			strpos(implode(',', array_keys($filter)), self::CF_PREFIX) === false)
+			strpos(implode(',', array_keys($filter ? $filter : [])), self::CF_PREFIX) === false)
 		{
 			return parent::search($criteria,$only_keys,$order_by,$extra_cols,$wildcard,$empty,$op,$start,$filter,$join,$need_full_no_count);
 		}