diff --git a/src/Illuminate/Validation/Validator.php b/src/Illuminate/Validation/Validator.php
index a2d1cfce320d..c44c5d5211b2 100755
--- a/src/Illuminate/Validation/Validator.php
+++ b/src/Illuminate/Validation/Validator.php
@@ -1026,7 +1026,7 @@ protected function callExtension($rule, $parameters)
     {
         $callback = $this->extensions[$rule];
 
-        if ($callback instanceof Closure) {
+        if (is_callable($callback)) {
             return call_user_func_array($callback, $parameters);
         } elseif (is_string($callback)) {
             return $this->callClassBasedExtension($callback, $parameters);