diff --git a/src/Illuminate/Cookie/Middleware/EncryptCookies.php b/src/Illuminate/Cookie/Middleware/EncryptCookies.php
index d67c7b6308bc..4d6c626eb9e5 100644
--- a/src/Illuminate/Cookie/Middleware/EncryptCookies.php
+++ b/src/Illuminate/Cookie/Middleware/EncryptCookies.php
@@ -118,7 +118,7 @@ protected function validateArray(string $key, array $value)
         $validated = [];
 
         foreach ($value as $index => $subValue) {
-            $validated[$index] = $this->validateValue("${key}[${index}]", $subValue);
+            $validated[$index] = $this->validateValue("{$key}[{$index}]", $subValue);
         }
 
         return $validated;