diff --git a/src/Services/AppsGoogleCom.php b/src/Services/AppsGoogleCom.php
index 4fbc6a4..ee88ff9 100644
--- a/src/Services/AppsGoogleCom.php
+++ b/src/Services/AppsGoogleCom.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/Services/GmailCom.php b/src/Services/GmailCom.php
index c79411a..6e399d3 100644
--- a/src/Services/GmailCom.php
+++ b/src/Services/GmailCom.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/Services/MultiDomain.php b/src/Services/MultiDomain.php
index 33f6a34..791cb28 100644
--- a/src/Services/MultiDomain.php
+++ b/src/Services/MultiDomain.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/Services/OutlookCom.php b/src/Services/OutlookCom.php
index b37f217..c185b9f 100644
--- a/src/Services/OutlookCom.php
+++ b/src/Services/OutlookCom.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/Services/TlenPl.php b/src/Services/TlenPl.php
index 5c12d10..1dec5c2 100644
--- a/src/Services/TlenPl.php
+++ b/src/Services/TlenPl.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/Services/Www33MailCom.php b/src/Services/Www33MailCom.php
index e1e2cd5..6750667 100644
--- a/src/Services/Www33MailCom.php
+++ b/src/Services/Www33MailCom.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/Services/YahooCom.php b/src/Services/YahooCom.php
index 60b05c7..bcfcc25 100644
--- a/src/Services/YahooCom.php
+++ b/src/Services/YahooCom.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Services;
 
 /**
diff --git a/src/TransparentEmail.php b/src/TransparentEmail.php
index 82d2ac3..517ff12 100644
--- a/src/TransparentEmail.php
+++ b/src/TransparentEmail.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail;
 
 use bkrukowski\TransparentEmail\Services\ServiceInterface;
diff --git a/tests/Services/AppsGoogleComTest.php b/tests/Services/AppsGoogleComTest.php
index 28c2d35..ee16fbd 100644
--- a/tests/Services/AppsGoogleComTest.php
+++ b/tests/Services/AppsGoogleComTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests\Services;
 
 use bkrukowski\TransparentEmail\Services\AppsGoogleCom;
diff --git a/tests/Services/GmailComTest.php b/tests/Services/GmailComTest.php
index 84a27e2..f371b75 100644
--- a/tests/Services/GmailComTest.php
+++ b/tests/Services/GmailComTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests\Services;
 
 use bkrukowski\TransparentEmail\Services\GmailCom;
diff --git a/tests/Services/MultiDomainTest.php b/tests/Services/MultiDomainTest.php
index 505cb96..9ff7911 100644
--- a/tests/Services/MultiDomainTest.php
+++ b/tests/Services/MultiDomainTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests\Services;
 
 use bkrukowski\TransparentEmail\Services\MultiDomain;
diff --git a/tests/Services/OutlookComTest.php b/tests/Services/OutlookComTest.php
index e826bc3..f53a4cc 100644
--- a/tests/Services/OutlookComTest.php
+++ b/tests/Services/OutlookComTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests\Services;
 
 use bkrukowski\TransparentEmail\Services\OutlookCom;
diff --git a/tests/Services/Www33MailComTest.php b/tests/Services/Www33MailComTest.php
index 2ace1aa..ddd7978 100644
--- a/tests/Services/Www33MailComTest.php
+++ b/tests/Services/Www33MailComTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests\Services;
 
 use bkrukowski\TransparentEmail\Services\Www33MailCom;
diff --git a/tests/Services/YahooComTest.php b/tests/Services/YahooComTest.php
index 69f8baa..ec2d47a 100644
--- a/tests/Services/YahooComTest.php
+++ b/tests/Services/YahooComTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests\Services;
 
 use bkrukowski\TransparentEmail\Services\YahooCom;
diff --git a/tests/TransparentEmailTest.php b/tests/TransparentEmailTest.php
index efa42f1..907c765 100644
--- a/tests/TransparentEmailTest.php
+++ b/tests/TransparentEmailTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace bkrukowski\TransparentEmail\Tests;
 
 use bkrukowski\TransparentEmail\ServiceCollector;