diff --git a/tests/Models/NullTaxCodeL11nTest.php b/tests/Models/NullTaxCodeL11nTest.php
index 06bfda1..f30e383 100644
--- a/tests/Models/NullTaxCodeL11nTest.php
+++ b/tests/Models/NullTaxCodeL11nTest.php
@@ -47,6 +47,6 @@ final class NullTaxCodeL11nTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullTaxCodeL11n(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullTaxCodeTest.php b/tests/Models/NullTaxCodeTest.php
index 3f331d5..fe079d2 100644
--- a/tests/Models/NullTaxCodeTest.php
+++ b/tests/Models/NullTaxCodeTest.php
@@ -47,6 +47,6 @@ final class NullTaxCodeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullTaxCode(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }