diff --git a/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php b/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php
index 45dc29d00dc7c490c4377af188b6ec3982f63160..a2be39a550cd7a7693ef3b4f438600e77055f254 100644
--- a/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php
+++ b/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php
@@ -36,7 +36,7 @@ class FieldsetFilter extends \Neomerx\JsonApi\Representation\FieldSetFilter
      */
     private function resolveValue($value)
     {
-        if (!is_string($value) && is_callable($value)) {
+        if ($value instanceof \Closure) {
             return $value();
         }