diff --git a/src/CallbackStream.php b/src/CallbackStream.php
index 83e52ed1..f1371202 100644
--- a/src/CallbackStream.php
+++ b/src/CallbackStream.php
@@ -155,7 +155,7 @@ public function getContents()
     {
         $callback = $this->detach();
 
-        return $callback ? $callback() : '';
+        return $callback ? call_user_fanc($callback) : '';
     }
 
     /**