diff --git a/src/Intervention/Image/Commands/Argument.php b/src/Intervention/Image/Commands/Argument.php
index 95b4b2f9..e64e8ac5 100644
--- a/src/Intervention/Image/Commands/Argument.php
+++ b/src/Intervention/Image/Commands/Argument.php
@@ -114,7 +114,7 @@ class Argument
                 $message = '%s accepts only array as argument %d.';
                 break;
             case 'closure':
-                $valid = is_a($value, \Closure::class);
+                $valid = is_a($value, '\Closure');
                 $message = '%s accepts only Closure as argument %d.';
                 break;
             case 'digit':