diff --git a/src/Concerns/Testable.php b/src/Concerns/Testable.php
index 347e3095..defdc8e2 100644
--- a/src/Concerns/Testable.php
+++ b/src/Concerns/Testable.php
@@ -293,7 +293,7 @@ trait Testable
             return $arguments;
         }
 
-        if (! $arguments[0] instanceof Closure) {
+        if (! isset($arguments[0]) || ! $arguments[0] instanceof Closure) {
             return $arguments;
         }