diff --git a/src/contracts/Validation/AbstractValidationStructWrapper.php b/src/contracts/Validation/AbstractValidationStructWrapper.php
index df7773222a..4ffdc057d4 100644
--- a/src/contracts/Validation/AbstractValidationStructWrapper.php
+++ b/src/contracts/Validation/AbstractValidationStructWrapper.php
@@ -4,6 +4,8 @@
  * @copyright Copyright (C) Ibexa AS. All rights reserved.
  * @license For full copyright and license information view LICENSE file distributed with this source code.
  */
+declare(strict_types=1);
+
 namespace Ibexa\Contracts\Core\Validation;
 
 use Symfony\Component\Validator\Constraints as Assert;
diff --git a/src/contracts/Validation/StructWrapperValidator.php b/src/contracts/Validation/StructWrapperValidator.php
index 4aa8b2885e..fbeb2c7ec3 100644
--- a/src/contracts/Validation/StructWrapperValidator.php
+++ b/src/contracts/Validation/StructWrapperValidator.php
@@ -4,6 +4,8 @@
  * @copyright Copyright (C) Ibexa AS. All rights reserved.
  * @license For full copyright and license information view LICENSE file distributed with this source code.
  */
+declare(strict_types=1);
+
 namespace Ibexa\Contracts\Core\Validation;
 
 use Symfony\Component\Validator\ConstraintViolation;
diff --git a/src/contracts/Validation/ValidationStructWrapperInterface.php b/src/contracts/Validation/ValidationStructWrapperInterface.php
index 8f39cf2b14..e68830894e 100644
--- a/src/contracts/Validation/ValidationStructWrapperInterface.php
+++ b/src/contracts/Validation/ValidationStructWrapperInterface.php
@@ -4,6 +4,8 @@
  * @copyright Copyright (C) Ibexa AS. All rights reserved.
  * @license For full copyright and license information view LICENSE file distributed with this source code.
  */
+declare(strict_types=1);
+
 namespace Ibexa\Contracts\Core\Validation;
 
 /**
diff --git a/tests/lib/Validation/StructWrapperValidatorTest.php b/tests/lib/Validation/StructWrapperValidatorTest.php
index 51f6d6f07a..e63923cb36 100644
--- a/tests/lib/Validation/StructWrapperValidatorTest.php
+++ b/tests/lib/Validation/StructWrapperValidatorTest.php
@@ -4,6 +4,8 @@
  * @copyright Copyright (C) Ibexa AS. All rights reserved.
  * @license For full copyright and license information view LICENSE file distributed with this source code.
  */
+declare(strict_types=1);
+
 namespace Ibexa\Tests\Core\Validation;
 
 use Ibexa\Contracts\Core\Validation\StructWrapperValidator;