diff --git a/src/Opis/Helper.php b/src/Opis/Helper.php
index c9323ef..a38c88a 100644
--- a/src/Opis/Helper.php
+++ b/src/Opis/Helper.php
@@ -1,10 +1,10 @@
 <?php
 
+declare(strict_types = 1);
 
 namespace Zfegg\ContentValidation\Opis;
 
-
 class Helper
 {
     const JSON_ALL_TYPES = ['string', 'integer', 'number', 'boolean', 'null', 'object', 'array'];
-}
\ No newline at end of file
+}
diff --git a/src/Opis/Resolver/TransformerResolver.php b/src/Opis/Resolver/TransformerResolver.php
index c7be79c..758b7e6 100644
--- a/src/Opis/Resolver/TransformerResolver.php
+++ b/src/Opis/Resolver/TransformerResolver.php
@@ -4,7 +4,6 @@
 
 namespace Zfegg\ContentValidation\Opis\Resolver;
 
-
 use Zfegg\ContentValidation\Opis\Helper;
 
 /**
diff --git a/test/Opis/TransformersParserTest.php b/test/Opis/TransformersParserTest.php
index 39ff03b..d32e8ad 100644
--- a/test/Opis/TransformersParserTest.php
+++ b/test/Opis/TransformersParserTest.php
@@ -14,7 +14,7 @@ class TransformersParserTest extends TestCase
 
     use SetupTrait;
 
-    public function json()
+    public function json(): array
     {
         return [
             ['123'],