diff --git a/Classes/Package.php b/Classes/Package.php
index 06bba5a..2335797 100644
--- a/Classes/Package.php
+++ b/Classes/Package.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace DigiComp\SettingValidator;
 
 /*
diff --git a/Classes/Validation/Validator/SettingsValidator.php b/Classes/Validation/Validator/SettingsValidator.php
index 8b825d8..46715de 100644
--- a/Classes/Validation/Validator/SettingsValidator.php
+++ b/Classes/Validation/Validator/SettingsValidator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace DigiComp\SettingValidator\Validation\Validator;
 
 /*
diff --git a/Migrations/Code/Version20170603120900.php b/Migrations/Code/Version20170603120900.php
index c162dd6..23ad8a3 100644
--- a/Migrations/Code/Version20170603120900.php
+++ b/Migrations/Code/Version20170603120900.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Neos\Flow\Core\Migrations;
 
 /**
diff --git a/Tests/Functional/Fixtures/TestObject.php b/Tests/Functional/Fixtures/TestObject.php
index 6f8e667..4d65558 100644
--- a/Tests/Functional/Fixtures/TestObject.php
+++ b/Tests/Functional/Fixtures/TestObject.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace DigiComp\SettingValidator\Tests\Functional\Fixtures;
 
 use Neos\Flow\Annotations as Flow;
diff --git a/Tests/Functional/Fixtures/TestValidationGroupsCustomObject.php b/Tests/Functional/Fixtures/TestValidationGroupsCustomObject.php
index b671e00..b07690f 100644
--- a/Tests/Functional/Fixtures/TestValidationGroupsCustomObject.php
+++ b/Tests/Functional/Fixtures/TestValidationGroupsCustomObject.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace DigiComp\SettingValidator\Tests\Functional\Fixtures;
 
 class TestValidationGroupsCustomObject
diff --git a/Tests/Functional/Fixtures/TestValidationGroupsDefaultObject.php b/Tests/Functional/Fixtures/TestValidationGroupsDefaultObject.php
index 30261b2..31eefbb 100644
--- a/Tests/Functional/Fixtures/TestValidationGroupsDefaultObject.php
+++ b/Tests/Functional/Fixtures/TestValidationGroupsDefaultObject.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace DigiComp\SettingValidator\Tests\Functional\Fixtures;
 
 class TestValidationGroupsDefaultObject
diff --git a/Tests/Functional/SettingsValidatorTest.php b/Tests/Functional/SettingsValidatorTest.php
index 4f07567..54b4764 100644
--- a/Tests/Functional/SettingsValidatorTest.php
+++ b/Tests/Functional/SettingsValidatorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace DigiComp\SettingValidator\Tests\Functional;
 
 use DigiComp\SettingValidator\Tests\Functional\Fixtures\TestObject;