diff --git a/src/QUI/ERP/Coupons/CodeGeneratorInterface.php b/src/QUI/ERP/Coupons/CodeGeneratorInterface.php
index 7918f69f1e75f5ad650a6738f8a453e8ff625ec4..b433d1f682558521f4b57b5f9d4a0bff7448306d 100644
--- a/src/QUI/ERP/Coupons/CodeGeneratorInterface.php
+++ b/src/QUI/ERP/Coupons/CodeGeneratorInterface.php
@@ -15,5 +15,5 @@ interface CodeGeneratorInterface
      * @param string $prefix (optional)
      * @return string
      */
-    public static function generate($prefix = '');
+    public static function generate(string $prefix = ''): string;
 }
diff --git a/src/QUI/ERP/Coupons/CodeGenerators/SimpleString.php b/src/QUI/ERP/Coupons/CodeGenerators/SimpleString.php
index 96a735fd7aae233f915b811b68b0b7ef73b5c840..d6f93435a480dcc2c9803ea5fabd54a8dfd95ce5 100644
--- a/src/QUI/ERP/Coupons/CodeGenerators/SimpleString.php
+++ b/src/QUI/ERP/Coupons/CodeGenerators/SimpleString.php
@@ -30,7 +30,7 @@ class SimpleString implements CodeGeneratorInterface
      * @return string
      * @throws Exception
      */
-    public static function generate($prefix = ''): string
+    public static function generate(string $prefix = ''): string
     {
         $characters = array_merge(
             range('A', 'Z'),
diff --git a/src/QUI/ERP/Coupons/CodeGenerators/Uuid.php b/src/QUI/ERP/Coupons/CodeGenerators/Uuid.php
index 662b3c23d6ef3e4bd3d8bf9884fdcdebbda94297..8a1497b6ca6486a56bcfd9222e7702050d72742c 100644
--- a/src/QUI/ERP/Coupons/CodeGenerators/Uuid.php
+++ b/src/QUI/ERP/Coupons/CodeGenerators/Uuid.php
@@ -13,7 +13,7 @@ class Uuid implements CodeGeneratorInterface
      * @param string $prefix (optional)
      * @return string
      */
-    public static function generate($prefix = ''): string
+    public static function generate(string $prefix = ''): string
     {
         return $prefix . UuidCreator::uuid1()->toString();
     }